/*-------------------------------------------------------------------------
*
* bufmgr.c
* buffer manager interface routines
*
* Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/storage/buffer/bufmgr.c
*
*-------------------------------------------------------------------------
*/
/*
* Principal entry points:
*
* ReadBuffer() -- find or create a buffer holding the requested page,
* and pin it so that no one can destroy it while this process
* is using it.
*
* StartReadBuffer() -- as above, with separate wait step
* StartReadBuffers() -- multiple block version
* WaitReadBuffers() -- second step of above
*
* ReleaseBuffer() -- unpin a buffer
*
* MarkBufferDirty() -- mark a pinned buffer's contents as "dirty".
* The disk write is delayed until buffer replacement or checkpoint.
*
* See also these files:
* freelist.c -- chooses victim for buffer replacement
* buf_table.c -- manages the buffer lookup table
*/
#include "postgres.h"
#include <sys/file.h>
#include <unistd.h>
#include "access/tableam.h"
#include "access/xloginsert.h"
#include "access/xlogutils.h"
#include "catalog/storage.h"
#include "catalog/storage_xlog.h"
#include "executor/instrument.h"
#include "lib/binaryheap.h"
#include "miscadmin.h"
#include "pg_trace.h"
#include "pgstat.h"
#include "postmaster/bgwriter.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
#include "storage/proc.h"
#include "storage/read_stream.h"
#include "storage/smgr.h"
#include "storage/standby.h"
#include "utils/memdebug.h"
#include "utils/ps_status.h"
#include "utils/rel.h"
#include "utils/resowner.h"
#include "utils/timestamp.h"
/* Note: these two macros only work on shared buffers, not local ones! */
#define BufHdrGetBlock(bufHdr) ((Block) (BufferBlocks + ((Size) (bufHdr)->buf_id) * BLCKSZ))
#define BufferGetLSN(bufHdr) (PageGetLSN(BufHdrGetBlock(bufHdr)))
/* Note: this macro only works on local buffers, not shared ones! */
#define LocalBufHdrGetBlock(bufHdr) \
LocalBufferBlockPointers[-((bufHdr)->buf_id + 2)]
/* Bits in SyncOneBuffer's return value */
#define BUF_WRITTEN 0x01
#define BUF_REUSABLE 0x02
#define RELS_BSEARCH_THRESHOLD 20
/*
* This is the size (in the number of blocks) above which we scan the
* entire buffer pool to remove the buffers for all the pages of relation
* being dropped. For the relations with size below this threshold, we find
* the buffers by doing lookups in BufMapping table.
*/
#define BUF_DROP_FULL_SCAN_THRESHOLD (uint64) (NBuffers / 32)
typedef struct PrivateRefCountEntry
{
Buffer buffer;
int32 refcount;
} PrivateRefCountEntry;
/* 64 bytes, about the size of a cache line on common systems */
#define REFCOUNT_ARRAY_ENTRIES 8
/*
* Status of buffers to checkpoint for a particular tablespace, used
* internally in BufferSync.
*/
typedef struct CkptTsStatus
{
/* oid of the tablespace */
Oid tsId;
/*
* Checkpoint progress for this tablespace. To make progress comparable
* between tablespaces the progress is, for each tablespace, measured as a
* number between 0 and the total number of to-be-checkpointed pages. Each
* page checkpointed in this tablespace increments this space's progress
* by progress_slice.
*/
float8 progress;
float8 progress_slice;
/* number of to-be checkpointed pages in this tablespace */
int num_to_scan;
/* already processed pages in this tablespace */
int num_scanned;
/* current offset in CkptBufferIds for this tablespace */
int index;
} CkptTsStatus;
/*
* Type for array used to sort SMgrRelations
*
* FlushRelationsAllBuffers shares the same comparator function with
* DropRelationsAllBuffers. Pointer to this struct and RelFileLocator must be
* compatible.
*/
typedef struct SMgrSortArray
{
RelFileLocator rlocator; /* This must be the first member */
SMgrRelation srel;
} SMgrSortArray;
/* GUC variables */
bool zero_damaged_pages = false;
int bgwriter_lru_maxpages = 100;
double bgwriter_lru_multiplier = 2.0;
bool track_io_timing = false;
/*
* How many buffers PrefetchBuffer callers should try to stay ahead of their
* ReadBuffer calls by. Zero means "never prefetch". This value is only used
* for buffers not belonging to tablespaces that have their
* effective_io_concurrency parameter set.
*/
int effective_io_concurrency = DEFAULT_EFFECTIVE_IO_CONCURRENCY;
/*
* Like effective_io_concurrency, but used by maintenance code paths that might
* benefit from a higher setting because they work on behalf of many sessions.
* Overridden by the tablespace setting of the same name.
*/
int maintenance_io_concurrency = DEFAULT_MAINTENANCE_IO_CONCURRENCY;
/*
* Limit on how many blocks should be handled in single I/O operations.
* StartReadBuffers() callers should respect it, as should other operations
* that call smgr APIs directly.
*/
int io_combine_limit = DEFAULT_IO_COMBINE_LIMIT;
/*
* GUC variables about triggering kernel writeback for buffers written; OS
* dependent defaults are set via the GUC mechanism.
*/
int checkpoint_flush_after = DEFAULT_CHECKPOINT_FLUSH_AFTER;
int bgwriter_flush_after = DEFAULT_BGWRITER_FLUSH_AFTER;
int backend_flush_after = DEFAULT_BACKEND_FLUSH_AFTER;
/* local state for LockBufferForCleanup */
static BufferDesc *PinCountWaitBuf = NULL;
/*
* Backend-Private refcount management:
*
* Each buffer also has a private refcount that keeps track of the number of
* times the buffer is pinned in the current process. This is so that the
* shared refcount needs to be modified only once if a buffer is pinned more
* than once by an individual backend. It's also used to check that no buffers
* are still pinned at the end of transactions and when exiting.
*
*
* To avoid - as we used to - requiring an array with NBuffers entries to keep
* track of local buffers, we use a small sequentially searched array
* (PrivateRefCountArray) and an overflow hash table (PrivateRefCountHash) to
* keep track of backend local pins.
*
* Until no more than REFCOUNT_ARRAY_ENTRIES buffers are pinned at once, all
* refcounts are kept track of in the array; after that, new array entries
* displace old ones into the hash table. That way a frequently used entry
* can't get "stuck" in the hashtable while infrequent ones clog the array.
*
* Note that in most scenarios the number of pinned buffers will not exceed
* REFCOUNT_ARRAY_ENTRIES.
*
*
* To enter a buffer into the refcount tracking mechanism first reserve a free
* entry using ReservePrivateRefCountEntry() and then later, if necessary,
* fill it with NewPrivateRefCountEntry(). That split lets us avoid doing
* memory allocations in NewPrivateRefCountEntry() which can be important
* because in some scenarios it's called with a spinlock held...
*/
static struct PrivateRefCountEntry PrivateRefCountArray[REFCOUNT_ARRAY_ENTRIES];
static HTAB *PrivateRefCountHash = NULL;
static int32 PrivateRefCountOverflowed = 0;
static uint32 PrivateRefCountClock = 0;
static PrivateRefCountEntry *ReservedRefCountEntry = NULL;
static void ReservePrivateRefCountEntry(void);
static PrivateRefCountEntry *NewPrivateRefCountEntry(Buffer buffer);
static PrivateRefCountEntry *GetPrivateRefCountEntry(Buffer buffer, bool do_move);
static inline int32 GetPrivateRefCount(Buffer buffer);
static void ForgetPrivateRefCountEntry(PrivateRefCountEntry *ref);
/* ResourceOwner callbacks to hold in-progress I/Os and buffer pins */
static void ResOwnerReleaseBufferIO(Datum res);
static char *ResOwnerPrintBufferIO(Datum res);
static void ResOwnerReleaseBufferPin(Datum res);
static char *ResOwnerPrintBufferPin(Datum res);
const ResourceOwnerDesc buffer_io_resowner_desc =
{
.name = "buffer io",
.release_phase = RESOURCE_RELEASE_BEFORE_LOCKS,
.release_priority = RELEASE_PRIO_BUFFER_IOS,
.ReleaseResource = ResOwnerReleaseBufferIO,
.DebugPrint = ResOwnerPrintBufferIO
};
const ResourceOwnerDesc buffer_pin_resowner_desc =
{
.name = "buffer pin",
.release_phase = RESOURCE_RELEASE_BEFORE_LOCKS,
.release_priority = RELEASE_PRIO_BUFFER_PINS,
.ReleaseResource = ResOwnerReleaseBufferPin,
.DebugPrint = ResOwnerPrintBufferPin
};
/*
* Ensure that the PrivateRefCountArray has sufficient space to store one more
* entry. This has to be called before using NewPrivateRefCountEntry() to fill
* a new entry - but it's perfectly fine to not use a reserved entry.
*/
static void
ReservePrivateRefCountEntry(void)
{
/* Already reserved (or freed), nothing to do */
if (ReservedRefCountEntry != NULL)
return;
/*
* First search for a free entry the array, that'll be sufficient in the
* majority of cases.
*/
{
int i;
for (i = 0; i < REFCOUNT_ARRAY_ENTRIES; i++)
{
PrivateRefCountEntry *res;
res = &PrivateRefCountArray[i];
if (res->buffer == InvalidBuffer)
{
ReservedRefCountEntry = res;
return;
}
}
}
/*
* No luck. All array entries are full. Move one array entry into the hash
* table.
*/
{
/*
* Move entry from the current clock position in the array into the
* hashtable. Use that slot.
*/
PrivateRefCountEntry *hashent;
bool found;
/* select victim slot */
ReservedRefCountEntry =
&PrivateRefCountArray[PrivateRefCountClock++ % REFCOUNT_ARRAY_ENTRIES];
/* Better be used, otherwise we shouldn't get here. */
Assert(ReservedRefCountEntry->buffer != InvalidBuffer);
/* enter victim array entry into hashtable */
hashent = hash_search(PrivateRefCountHash,
&(ReservedRefCountEntry->buffer),
HASH_ENTER,
&found);
Assert(!found);
hashent->refcount = ReservedRefCountEntry->refcount;
/* clear the now free array slot */
ReservedRefCountEntry->buffer = InvalidBuffer;
ReservedRefCountEntry->refcount = 0;
PrivateRefCountOverflowed++;
}
}
/*
* Fill a previously reserved refcount entry.
*/
static PrivateRefCountEntry *
NewPrivateRefCountEntry(Buffer buffer)
{
PrivateRefCountEntry *res;
/* only allowed to be called when a reservation has been made */
Assert(ReservedRefCountEntry != NULL);
/* use up the reserved entry */
res = ReservedRefCountEntry;
ReservedRefCountEntry = NULL;
/* and fill it */
res->buffer = buffer;
res->refcount = 0;
return res;
}
/*
* Return the PrivateRefCount entry for the passed buffer.
*
* Returns NULL if a buffer doesn't have a refcount entry. Otherwise, if
* do_move is true, and the entry resides in the hashtable the entry is
* optimized for frequent access by moving it to the array.
*/
static PrivateRefCountEntry *
GetPrivateRefCountEntry(Buffer buffer, bool do_move)
{
PrivateRefCountEntry *res;
int i;
Assert(BufferIsValid(buffer));
Assert(!BufferIsLocal(buffer));
/*
* First search for references in the array, that'll be sufficient in the
* majority of cases.
*/
for (i = 0; i < REFCOUNT_ARRAY_ENTRIES; i++)
{
res = &PrivateRefCountArray[i];
if (res->buffer == buffer)
return res;
}
/*
* By here we know that the buffer, if already pinned, isn't residing in
* the array.
*
* Only look up the buffer in the hashtable if we've previously overflowed
* into it.
*/
if (PrivateRefCountOverflowed == 0)
return NULL;
res = hash_search(PrivateRefCountHash, &buffer, HASH_FIND, NULL);
if (res == NULL)
return NULL;
else if (!do_move)
{
/* caller doesn't want us to move the hash entry into the array */
return res;
}
else
{
/* move buffer from hashtable into the free array slot */
bool found;
PrivateRefCountEntry *free;
/* Ensure there's a free array slot */
ReservePrivateRefCountEntry();
/* Use up the reserved slot */
Assert(ReservedRefCountEntry != NULL);
free = ReservedRefCountEntry;
ReservedRefCountEntry = NULL;
Assert(free->buffer == InvalidBuffer);
/* and fill it */
free->buffer = buffer;
free->refcount = res->refcount;
/* delete from hashtable */
hash_search(PrivateRefCountHash, &buffer, HASH_REMOVE, &found);
Assert(found);
Assert(PrivateRefCountOverflowed > 0);
PrivateRefCountOverflowed--;
return free;
}
}
/*
* Returns how many times the passed buffer is pinned by this backend.
*
* Only works for shared memory buffers!
*/
static inline int32
GetPrivateRefCount(Buffer buffer)
{
PrivateRefCountEntry *ref;
Assert(BufferIsValid(buffer));
Assert(!BufferIsLocal(buffer));
/*
* Not moving the entry - that's ok for the current users, but we might
* want to change this one day.
*/
ref = GetPrivateRefCountEntry(buffer, false);
if (ref == NULL)
return 0;
return ref->refcount;
}
/*
* Release resources used to track the reference count of a buffer which we no
* longer have pinned and don't want to pin again immediately.
*/
static void
ForgetPrivateRefCountEntry(PrivateRefCountEntry *ref)
{
Assert(ref->refcount == 0);
if (ref >= &PrivateRefCountArray[0] &&
ref < &PrivateRefCountArray[REFCOUNT_ARRAY_ENTRIES])
{
ref->buffer = InvalidBuffer;
/*
* Mark the just used entry as reserved - in many scenarios that
* allows us to avoid ever having to search the array/hash for free
* entries.
*/
ReservedRefCountEntry = ref;
}
else
{
bool found;
Buffer buffer = ref->buffer;
hash_search(PrivateRefCountHash, &buffer, HASH_REMOVE, &found);
Assert(found);
Assert(PrivateRefCountOverflowed > 0);
PrivateRefCountOverflowed--;
}
}
/*
* BufferIsPinned
* True iff the buffer is pinned (also checks for valid buffer number).
*
* NOTE: what we check here is that *this* backend holds a pin on
* the buffer. We do not care whether some other backend does.
*/
#define BufferIsPinned(bufnum) \
( \
!BufferIsValid(bufnum) ? \
false \
: \
BufferIsLocal(bufnum) ? \
(LocalRefCount[-(bufnum) - 1] > 0) \
: \
(GetPrivateRefCount(bufnum) > 0) \
)
static Buffer ReadBuffer_common(Relation rel,
SMgrRelation smgr, char smgr_persistence,
ForkNumber forkNum, BlockNumber blockNum,
ReadBufferMode mode, BufferAccessStrategy strategy);
static BlockNumber ExtendBufferedRelCommon(BufferManagerRelation bmr,
ForkNumber fork,
BufferAccessStrategy strategy,
uint32 flags,
uint32 extend_by,
BlockNumber extend_upto,
Buffer *buffers,
uint32 *extended_by);
static BlockNumber ExtendBufferedRelShared(BufferManagerRelation bmr,
ForkNumber fork,
BufferAccessStrategy strategy,
uint32 flags,
uint32 extend_by,
BlockNumber extend_upto,
Buffer *buffers,
uint32 *extended_by);
static bool PinBuffer(BufferDesc *buf, BufferAccessStrategy strategy);
static void PinBuffer_Locked(BufferDesc *buf);
static void UnpinBuffer(BufferDesc *buf);
static void UnpinBufferNoOwner(BufferDesc *buf);
static void BufferSync(int flags);
static uint32 WaitBufHdrUnlocked(BufferDesc *buf);
static int SyncOneBuffer(int buf_id, bool skip_recently_used,
WritebackContext *wb_context);
static void WaitIO(BufferDesc *buf);
static bool StartBufferIO(BufferDesc *buf, bool forInput, bool nowait);
static void TerminateBufferIO(BufferDesc *buf, bool clear_dirty,
uint32 set_flag_bits, bool forget_owner);
static void AbortBufferIO(Buffer buffer);
static void shared_buffer_write_error_callback(void *arg);
static void local_buffer_write_error_callback(void *arg);
static inline BufferDesc *BufferAlloc(SMgrRelation smgr,
char relpersistence,
ForkNumber forkNum,
BlockNumber blockNum,
BufferAccessStrategy strategy,
bool *foundPtr, IOContext io_context);
static Buffer GetVictimBuffer(BufferAccessStrategy strategy, IOContext io_context);
static void FlushBuffer(BufferDesc *buf, SMgrRelation reln,
IOObject io_object, IOContext io_context);
static void FindAndDropRelationBuffers(RelFileLocator rlocator,
ForkNumber forkNum,
BlockNumber nForkBlock,
BlockNumber firstDelBlock);
static void RelationCopyStorageUsingBuffer(RelFileLocator srclocator,
RelFileLocator dstlocator,
ForkNumber forkNum, bool permanent);
static void AtProcExit_Buffers(int code, Datum arg);
static void CheckForBufferLeaks(void);
static int rlocator_comparator(const void *p1, const void *p2);
static inline int buffertag_comparator(const BufferTag *ba, const BufferTag *bb);
static inline int ckpt_buforder_comparator(const CkptSortItem *a, const CkptSortItem *b);
static int ts_ckpt_progress_comparator(Datum a, Datum b, void *arg);
/*
* Implementation of PrefetchBuffer() for shared buffers.
*/
PrefetchBufferResult
PrefetchSharedBuffer(SMgrRelation smgr_reln,
ForkNumber forkNum,
BlockNumber blockNum)
{
PrefetchBufferResult result = {InvalidBuffer, false};
BufferTag newTag; /* identity of requested block */
uint32 newHash; /* hash value for newTag */
LWLock *newPartitionLock; /* buffer partition lock for it */
int buf_id;
Assert(BlockNumberIsValid(blockNum));
/* create a tag so we can lookup the buffer */
InitBufferTag(&newTag, &smgr_reln->smgr_rlocator.locator,
forkNum, blockNum);
/* determine its hash code and partition lock ID */
newHash = BufTableHashCode(&newTag);
newPartitionLock = BufMappingPartitionLock(newHash);
/* see if the block is in the buffer pool already */
LWLockAcquire(newPartitionLock, LW_SHARED);
buf_id = BufTableLookup(&newTag, newHash);
LWLockRelease(newPartitionLock);
/* If not in buffers, initiate prefetch */
if (buf_id < 0)
{
#ifdef USE_PREFETCH
/*
* Try to initiate an asynchronous read. This returns false in
* recovery if the relation file doesn't exist.
*/
if ((io_direct_flags & IO_DIRECT_DATA) == 0 &&
smgrprefetch(smgr_reln, forkNum, blockNum, 1))
{
result.initiated_io = true;
}
#endif /* USE_PREFETCH */
}
else
{
/*
* Report the buffer it was in at that time. The caller may be able
* to avoid a buffer table lookup, but it's not pinned and it must be
* rechecked!
*/
result.recent_buffer = buf_id + 1;
}
/*
* If the block *is* in buffers, we do nothing. This is not really ideal:
* the block might be just about to be evicted, which would be stupid
* since we know we are going to need it soon. But the only easy answer
* is to bump the usage_count, which does not seem like a great solution:
* when the caller does ultimately touch the block, usage_count would get
* bumped again, resulting in too much favoritism for blocks that are
* involved in a prefetch sequence. A real fix would involve some
* additional per-buffer state, and it's not clear that there's enough of
* a problem to justify that.
*/
return result;
}
/*
* PrefetchBuffer -- initiate asynchronous read of a block of a relation
*
* This is named by analogy to ReadBuffer but doesn't actually allocate a
* buffer. Instead it tries to ensure that a future ReadBuffer for the given
* block will not be delayed by the I/O. Prefetching is optional.
*
* There are three possible outcomes:
*
* 1. If the block is already cached, the result includes a valid buffer that
* could be used by the caller to avoid the need for a later buffer lookup, but
* it's not pinned, so the caller must recheck it.
*
* 2. If the kernel has been asked to initiate I/O, the initiated_io member is
* true. Currently there is no way to know if the data was already cached by
* the kernel and therefore didn't really initiate I/O, and no way to know when
* the I/O completes other than using synchronous ReadBuffer().
*
* 3. Otherwise, the buffer wasn't already cached by PostgreSQL, and
* USE_PREFETCH is not defined (this build doesn't support prefetching due to
* lack of a kernel facility), direct I/O is enabled, or the underlying
* relation file wasn't found and we are in recovery. (If the relation file
* wasn't found and we are not in recovery, an error is raised).
*/
PrefetchBufferResult
PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum)
{
Assert(RelationIsValid(reln));
Assert(BlockNumberIsValid(blockNum));
if (RelationUsesLocalBuffers(reln))
{
/* see comments in ReadBufferExtended */
if (RELATION_IS_OTHER_TEMP(reln))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot access temporary tables of other sessions")));
/* pass it off to localbuf.c */
return PrefetchLocalBuffer(RelationGetSmgr(reln), forkNum, blockNum);
}
else
{
/* pass it to the shared buffer version */
return PrefetchSharedBuffer(RelationGetSmgr(reln), forkNum, blockNum);
}
}
/*
* ReadRecentBuffer -- try to pin a block in a recently observed buffer
*
* Compared to ReadBuffer(), this avoids a buffer mapping lookup when it's
* successful. Return true if the buffer is valid and still has the expected
* tag. In that case, the buffer is pinned and the usage count is bumped.
*/
bool
ReadRecentBuffer(RelFileLocator rlocator, ForkNumber forkNum, BlockNumber blockNum,
Buffer recent_buffer)
{
BufferDesc *bufHdr;
BufferTag tag;
uint32 buf_state;
bool have_private_ref;
Assert(BufferIsValid(recent_buffer));
ResourceOwnerEnlarge(CurrentResourceOwner);
ReservePrivateRefCountEntry();
InitBufferTag(&tag, &rlocator, forkNum, blockNum);
if (BufferIsLocal(recent_buffer))
{
int b = -recent_buffer - 1;
bufHdr = GetLocalBufferDescriptor(b);
buf_state = pg_atomic_read_u32(&bufHdr->state);
/* Is it still valid and holding the right tag? */
if ((buf_state & BM_VALID) && BufferTagsEqual(&tag, &bufHdr->tag))
{
PinLocalBuffer(bufHdr, true);
pgBufferUsage.local_blks_hit++;
return true;
}
}
else
{
bufHdr = GetBufferDescriptor(recent_buffer - 1);
have_private_ref = GetPrivateRefCount(recent_buffer) > 0;
/*
* Do we already have this buffer pinned with a private reference? If
* so, it must be valid and it is safe to check the tag without
* locking. If not, we have to lock the header first and then check.
*/
if (have_private_ref)
buf_state = pg_atomic_read_u32(&bufHdr->state);
else
buf_state = LockBufHdr(bufHdr);
if ((buf_state & BM_VALID) && BufferTagsEqual(&tag, &bufHdr->tag))
{
/*
* It's now safe to pin the buffer. We can't pin first and ask
* questions later, because it might confuse code paths like
* InvalidateBuffer() if we pinned a random non-matching buffer.
*/
if (have_private_ref)
PinBuffer(bufHdr, NULL); /* bump pin count */
else
PinBuffer_Locked(bufHdr); /* pin for first time */
pgBufferUsage.shared_blks_hit++;
return true;
}
/* If we locked the header above, now unlock. */
if (!have_private_ref)
UnlockBufHdr(bufHdr, buf_state);
}
return false;
}
/*
* ReadBuffer -- a shorthand for ReadBufferExtended, for reading from main
* fork with RBM_NORMAL mode and default strategy.
*/
Buffer
ReadBuffer(Relation reln, BlockNumber blockNum)
{
return ReadBufferExtended(reln, MAIN_FORKNUM, blockNum, RBM_NORMAL, NULL);
}
/*
* ReadBufferExtended -- returns a buffer containing the requested
* block of the requested relation. If the blknum
* requested is P_NEW, extend the relation file and
* allocate a new block. (Caller is responsible for
* ensuring that only one backend tries to extend a
* relation at the same time!)
*
* Returns: the buffer number for the buffer containing
* the block read. The returned buffer has been pinned.
* Does not return on error --- elog's instead.
*
* Assume when this function is called, that reln has been opened already.
*
* In RBM_NORMAL mode, the page is read from disk, and the page header is
* validated. An error is thrown if the page header is not valid. (But
* note that an all-zero page is considered "valid"; see
* PageIsVerifiedExtended().)
*
* RBM_ZERO_ON_ERROR is like the normal mode, but if the page header is not
* valid, the page is zeroed instead of throwing an error. This is intended
* for non-critical data, where the caller is prepared to repair errors.
*
* In RBM_ZERO_AND_LOCK mode, if the page isn't in buffer cache already, it's
* filled with zeros instead of reading it from disk. Useful when the caller
* is going to fill the page from scratch, since this saves I/O and avoids
* unnecessary failure if the page-on-disk has corrupt page headers.
* The page is returned locked to ensure that the caller has a chance to
* initialize the page before it's made visible to others.
* Caution: do not use this mode to read a page that is beyond the relation's
* current physical EOF; that is likely to cause problems in md.c when
* the page is modified and written out. P_NEW is OK, though.
*
* RBM_ZERO_AND_CLEANUP_LOCK is the same as RBM_ZERO_AND_LOCK, but acquires
* a cleanup-strength lock on the page.
*
* RBM_NORMAL_NO_LOG mode is treated the same as RBM_NORMAL here.
*
* If strategy is not NULL, a nondefault buffer access strategy is used.
* See buffer/README for details.
*/
inline Buffer
ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum,
ReadBufferMode mode, BufferAccessStrategy strategy)
{
Buffer buf;
/*
* Reject attempts to read non-local temporary relations; we would be
* likely to get wrong data since we have no visibility into the owning
* session's local buffers.
*/
if (RELATION_IS_OTHER_TEMP(reln))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot access temporary tables of other sessions")));
/*
* Read the buffer, and update pgstat counters to reflect a cache hit or
* miss.
*/
buf = ReadBuffer_common(reln, RelationGetSmgr(reln), 0,
forkNum, blockNum, mode, strategy);
return buf;
}
/*
* ReadBufferWithoutRelcache -- like ReadBufferExtended, but doesn't require
* a relcache entry for the relation.
*
* Pass permanent = true for a RELPERSISTENCE_PERMANENT relation, and
* permanent = false for a RELPERSISTENCE_UNLOGGED relation. This function
* cannot be used for temporary relations (and making that work might be
* difficult, unless we only want to read temporary relations for our own
* ProcNumber).
*/
Buffer
ReadBufferWithoutRelcache(RelFileLocator rlocator, ForkNumber forkNum,
BlockNumber blockNum, ReadBufferMode mode,
BufferAccessStrategy strategy, bool permanent)
{
SMgrRelation smgr = smgropen(rlocator, INVALID_PROC_NUMBER);
return ReadBuffer_common(NULL, smgr,
permanent ? RELPERSISTENCE_PERMANENT : RELPERSISTENCE_UNLOGGED,
forkNum, blockNum,
mode, strategy);
}
/*
* Convenience wrapper around ExtendBufferedRelBy() extending by one block.
*/
Buffer
ExtendBufferedRel(BufferManagerRelation bmr,
ForkNumber forkNum,
BufferAccessStrategy strategy,
uint32 flags)
{
Buffer buf;
uint32 extend_by = 1;
ExtendBufferedRelBy(bmr, forkNum, strategy, flags, extend_by,
&buf, &extend_by);
return buf;
}
/*
* Extend relation by multiple blocks.
*
* Tries to extend the relation by extend_by blocks. Depending on the
* availability of resources the relation may end up being extended by a
* smaller number of pages (unless an error is thrown, always by at least one
* page). *extended_by is updated to the number of pages the relation has been
* extended to.
*
* buffers needs to be an array that is at least extend_by long. Upon
* completion, the first extend_by array elements will point to a pinned
* buffer.
*
* If EB_LOCK_FIRST is part of flags, the first returned buffer is
* locked. This is useful for callers that want a buffer that is guaranteed to
* be empty.
*/
BlockNumber
ExtendBufferedRelBy(BufferManagerRelation bmr,
ForkNumber fork,
BufferAccessStrategy strategy,
uint32 flags,
uint32 extend_by,
Buffer *buffers,
uint32 *extended_by)
{
Assert((bmr.rel != NULL) != (bmr.smgr != NULL));
Assert(bmr.smgr == NULL || bmr.relpersistence != 0);
Assert(extend_by > 0);
if (bmr.smgr == NULL)
{
bmr.smgr = RelationGetSmgr(bmr.rel);
bmr.relpersistence = bmr.rel->rd_rel->relpersistence;
}
return ExtendBufferedRelCommon(bmr, fork, strategy, flags,
extend_by, InvalidBlockNumber,
buffers, extended_by);
}
/*
* Extend the relation so it is at least extend_to blocks large, return buffer
* (extend_to - 1).
*
* This is useful for callers that want to write a specific page, regardless
* of the current size of the relation (e.g. useful for visibilitymap and for
* crash recovery).
*/
Buffer
ExtendBufferedRelTo(BufferManagerRelation bmr,
ForkNumber fork,
BufferAccessStrategy strategy,
uint32 flags,
BlockNumber extend_to,
ReadBufferMode mode)
{
BlockNumber current_size;
uint32 extended_by = 0;
Buffer buffer = InvalidBuffer;
Buffer buffers[64];
Assert((bmr.rel != NULL) != (bmr.smgr != NULL));
Assert(bmr.smgr == NULL || bmr.relpersistence != 0);
Assert(extend_to != InvalidBlockNumber && extend_to > 0);
if (bmr.smgr == NULL)
{
bmr.smgr = RelationGetSmgr(bmr.rel);
bmr.relpersistence = bmr.rel->rd_rel->relpersistence;
}
/*
* If desired, create the file if it doesn't exist. If
* smgr_cached_nblocks[fork] is positive then it must exist, no need for
* an smgrexists call.
*/
if ((flags & EB_CREATE_FORK_IF_NEEDED) &&
(bmr.smgr->smgr_cached_nblocks[fork] == 0 ||
bmr.smgr->smgr_cached_nblocks[fork] == InvalidBlockNumber) &&
!smgrexists(bmr.smgr, fork))
{
LockRelationForExtension(bmr.rel, ExclusiveLock);
/* recheck, fork might have been created concurrently */
if (!smgrexists(bmr.smgr, fork))
smgrcreate(bmr.smgr, fork, flags & EB_PERFORMING_RECOVERY);
UnlockRelationForExtension(bmr.rel, ExclusiveLock);
}
/*
* If requested, invalidate size cache, so that smgrnblocks asks the
* kernel.
*/
if (flags & EB_CLEAR_SIZE_CACHE)
bmr.smgr->smgr_cached_nblocks[fork] = InvalidBlockNumber;
/*
* Estimate how many pages we'll need to extend by. This avoids acquiring
* unnecessarily many victim buffers.
*/
current_size = smgrnblocks(bmr.smgr, fork);
/*
* Since no-one else can be looking at the page contents yet, there is no
* difference between an exclusive lock and a cleanup-strength lock. Note
* that we pass the original mode to ReadBuffer_common() below, when
* falling back to reading the buffer to a concurrent relation extension.
*/
if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
flags |= EB_LOCK_TARGET;
while (current_size < extend_to)
{
uint32 num_pages = lengthof(buffers);
BlockNumber first_block;
if ((uint64) current_size + num_pages > extend_to)
num_pages = extend_to - current_size;
first_block = ExtendBufferedRelCommon(bmr, fork, strategy, flags,
num_pages, extend_to,
buffers, &extended_by);
current_size = first_block + extended_by;
Assert(num_pages != 0 || current_size >= extend_to);
for (uint32 i = 0; i < extended_by; i++)
{
if (first_block + i != extend_to - 1)
ReleaseBuffer(buffers[i]);
else
buffer = buffers[i];
}
}
/*
* It's possible that another backend concurrently extended the relation.
* In that case read the buffer.
*
* XXX: Should we control this via a flag?
*/
if (buffer == InvalidBuffer)
{
Assert(extended_by == 0);
buffer = ReadBuffer_common(bmr.rel, bmr.smgr, bmr.relpersistence,
fork, extend_to - 1, mode, strategy);
}
return buffer;
}
/*
* Lock and optionally zero a buffer, as part of the implementation of
* RBM_ZERO_AND_LOCK or RBM_ZERO_AND_CLEANUP_LOCK. The buffer must be already
* pinned. If the buffer is not already valid, it is zeroed and made valid.
*/
static void
ZeroAndLockBuffer(Buffer buffer, ReadBufferMode mode, bool already_valid)
{
BufferDesc *bufHdr;
bool need_to_zero;
bool isLocalBuf = BufferIsLocal(buffer);
Assert(mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK);
if (already_valid)
{
/*
* If the caller already knew the buffer was valid, we can skip some
* header interaction. The caller just wants to lock the buffer.
*/
need_to_zero = false;
}
else if (isLocalBuf)
{
/* Simple case for non-shared buffers. */
bufHdr = GetLocalBufferDescriptor(-buffer - 1);
need_to_zero = (pg_atomic_read_u32(&bufHdr->state) & BM_VALID) == 0;
}
else
{
/*
* Take BM_IO_IN_PROGRESS, or discover that BM_VALID has been set
* concurrently. Even though we aren't doing I/O, that ensures that
* we don't zero a page that someone else has pinned. An exclusive
* content lock wouldn't be enough, because readers are allowed to
* drop the content lock after determining that a tuple is visible
* (see buffer access rules in README).
*/
bufHdr = GetBufferDescriptor(buffer - 1);
need_to_zero = StartBufferIO(bufHdr, true, false);
}
if (need_to_zero)
{
memset(BufferGetPage(buffer), 0, BLCKSZ);
/*
* Grab the buffer content lock before marking the page as valid, to
* make sure that no other backend sees the zeroed page before the
* caller has had a chance to initialize it.
*
* Since no-one else can be looking at the page contents yet, there is
* no difference between an exclusive lock and a cleanup-strength
* lock. (Note that we cannot use LockBuffer() or
* LockBufferForCleanup() here, because they assert that the buffer is
* already valid.)
*/
if (!isLocalBuf)
LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_EXCLUSIVE);
if (isLocalBuf)
{
/* Only need to adjust flags */
uint32 buf_state = pg_atomic_read_u32(&bufHdr->state);
buf_state |= BM_VALID;
pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
}
else
{
/* Set BM_VALID, terminate IO, and wake up any waiters */
TerminateBufferIO(bufHdr, false, BM_VALID, true);
}
}
else if (!isLocalBuf)
{
/*
* The buffer is valid, so we can't zero it. The caller still expects
* the page to be locked on return.
*/
if (mode == RBM_ZERO_AND_LOCK)
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
else
LockBufferForCleanup(buffer);
}
}
/*
* Pin a buffer for a given block. *foundPtr is set to true if the block was
* already present, or false if more work is required to either read it in or
* zero it.
*/
static pg_attribute_always_inline Buffer
PinBufferForBlock(Relation rel,
SMgrRelation smgr,
char persistence,
ForkNumber forkNum,
BlockNumber blockNum,
BufferAccessStrategy strategy,
bool *foundPtr)
{
BufferDesc *bufHdr;
IOContext io_context;
IOObject io_object;
Assert(blockNum != P_NEW);
/* Persistence should be set before */
Assert((persistence == RELPERSISTENCE_TEMP ||
persistence == RELPERSISTENCE_PERMANENT ||
persistence == RELPERSISTENCE_UNLOGGED));
if (persistence == RELPERSISTENCE_TEMP)
{
io_context = IOCONTEXT_NORMAL;
io_object = IOOBJECT_TEMP_RELATION;
}
else
{
io_context = IOContextForStrategy(strategy);
io_object = IOOBJECT_RELATION;
}
TRACE_POSTGRESQL_BUFFER_READ_START(forkNum, blockNum,
smgr->smgr_rlocator.locator.spcOid,
smgr->smgr_rlocator.locator.dbOid,
smgr->smgr_rlocator.locator.relNumber,
smgr->smgr_rlocator.backend);
if (persistence == RELPERSISTENCE_TEMP)
{
bufHdr = LocalBufferAlloc(smgr, forkNum, blockNum, foundPtr);
if (*foundPtr)
pgBufferUsage.local_blks_hit++;
}
else
{
bufHdr = BufferAlloc(smgr, persistence, forkNum, blockNum,
strategy, foundPtr, io_context);
if (*foundPtr)
pgBufferUsage.shared_blks_hit++;
}
if (rel)
{
/*
* While pgBufferUsage's "read" counter isn't bumped unless we reach
* WaitReadBuffers() (so, not for hits, and not for buffers that are
* zeroed instead), the per-relation stats always count them.
*/
pgstat_count_buffer_read(rel);
if (*foundPtr)
pgstat_count_buffer_hit(rel);
}
if (*foundPtr)
{
pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1);
if (VacuumCostActive)
VacuumCostBalance += VacuumCostPageHit;
TRACE_POSTGRESQL_BUFFER_READ_DONE(forkNum, blockNum,
smgr->smgr_rlocator.locator.spcOid,
smgr->smgr_rlocator.locator.dbOid,
smgr->smgr_rlocator.locator.relNumber,
smgr->smgr_rlocator.backend,
true);
}
return BufferDescriptorGetBuffer(bufHdr);
}
/*
* ReadBuffer_common -- common logic for all ReadBuffer variants
*
* smgr is required, rel is optional unless using P_NEW.
*/
static pg_attribute_always_inline Buffer
ReadBuffer_common(Relation rel, SMgrRelation smgr, char smgr_persistence,
ForkNumber forkNum,
BlockNumber blockNum, ReadBufferMode mode,
BufferAccessStrategy strategy)
{
ReadBuffersOperation operation;
Buffer buffer;
int flags;
char persistence;
/*
* Backward compatibility path, most code should use ExtendBufferedRel()
* instead, as acquiring the extension lock inside ExtendBufferedRel()
* scales a lot better.
*/
if (unlikely(blockNum == P_NEW))
{
uint32 flags = EB_SKIP_EXTENSION_LOCK;
/*
* Since no-one else can be looking at the page contents yet, there is
* no difference between an exclusive lock and a cleanup-strength
* lock.
*/
if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
flags |= EB_LOCK_FIRST;
return ExtendBufferedRel(BMR_REL(rel), forkNum, strategy, flags);
}
if (rel)
persistence = rel->rd_rel->relpersistence;
else
persistence = smgr_persistence;
if (unlikely(mode == RBM_ZERO_AND_CLEANUP_LOCK ||
mode == RBM_ZERO_AND_LOCK))
{
bool found;
buffer = PinBufferForBlock(rel, smgr, persistence,
forkNum, blockNum, strategy, &found);
ZeroAndLockBuffer(buffer, mode, found);
return buffer;
}
if (mode == RBM_ZERO_ON_ERROR)
flags = READ_BUFFERS_ZERO_ON_ERROR;
else
flags = 0;
operation.smgr = smgr;
operation.rel = rel;
operation.persistence = persistence;
operation.forknum = forkNum;
operation.strategy = strategy;
if (StartReadBuffer(&operation,
&buffer,
blockNum,
flags))
WaitReadBuffers(&operation);
return buffer;
}
static pg_attribute_always_inline bool
StartReadBuffersImpl(ReadBuffersOperation *operation,
Buffer *buffers,
BlockNumber blockNum,
int *nblocks,
int flags)
{
int actual_nblocks = *nblocks;
int io_buffers_len = 0;
int maxcombine = 0;
Assert(*nblocks > 0);
Assert(*nblocks <= MAX_IO_COMBINE_LIMIT);
for (int i = 0; i < actual_nblocks; ++i)
{
bool found;
buffers[i] = PinBufferForBlock(operation->rel,
operation->smgr,
operation->persistence,
operation->forknum,
blockNum + i,
operation->strategy,
&found);
if (found)
{
/*
* Terminate the read as soon as we get a hit. It could be a
* single buffer hit, or it could be a hit that follows a readable
* range. We don't want to create more than one readable range,
* so we stop here.
*/
actual_nblocks = i + 1;
break;
}
else
{
/* Extend the readable range to cover this block. */
io_buffers_len++;
/*
* Check how many blocks we can cover with the same IO. The smgr
* implementation might e.g. be limited due to a segment boundary.
*/
if (i == 0 && actual_nblocks > 1)
{
maxcombine = smgrmaxcombine(operation->smgr,
operation->forknum,
blockNum);
if (unlikely(maxcombine < actual_nblocks))
{
elog(DEBUG2, "limiting nblocks at %u from %u to %u",
blockNum, actual_nblocks, maxcombine);
actual_nblocks = maxcombine;
}
}
}
}
*nblocks = actual_nblocks;
if (likely(io_buffers_len == 0))
return false;
/* Populate information needed for I/O. */
operation->buffers = buffers;
operation->blocknum = blockNum;
operation->flags = flags;
operation->nblocks = actual_nblocks;
operation->io_buffers_len = io_buffers_len;
if (flags & READ_BUFFERS_ISSUE_ADVICE)
{
/*
* In theory we should only do this if PinBufferForBlock() had to
* allocate new buffers above. That way, if two calls to
* StartReadBuffers() were made for the same blocks before
* WaitReadBuffers(), only the first would issue the advice. That'd be
* a better simulation of true asynchronous I/O, which would only
* start the I/O once, but isn't done here for simplicity. Note also
* that the following call might actually issue two advice calls if we
* cross a segment boundary; in a true asynchronous version we might
* choose to process only one real I/O at a time in that case.
*/
smgrprefetch(operation->smgr,
operation->forknum,
blockNum,
operation->io_buffers_len);
}
/* Indicate that WaitReadBuffers() should be called. */
return true;
}
/*
* Begin reading a range of blocks beginning at blockNum and extending for
* *nblocks. On return, up to *nblocks pinned buffers holding those blocks
* are written into the buffers array, and *nblocks is updated to contain the
* actual number, which may be fewer than requested. Caller sets some of the
* members of operation; see struct definition.
*
* If false is returned, no I/O is necessary. If true is returned, one I/O
* has been started, and WaitReadBuffers() must be called with the same
* operation object before the buffers are accessed. Along with the operation
* object, the caller-supplied array of buffers must remain valid until
* WaitReadBuffers() is called.
*
* Currently the I/O is only started with optional operating system advice if
* requested by the caller with READ_BUFFERS_ISSUE_ADVICE, and the real I/O
* happens synchronously in WaitReadBuffers(). In future work, true I/O could
* be initiated here.
*/
bool
StartReadBuffers(ReadBuffersOperation *operation,
Buffer *buffers,
BlockNumber blockNum,
int *nblocks,
int flags)
{
return StartReadBuffersImpl(operation, buffers, blockNum, nblocks, flags);
}
/*
* Single block version of the StartReadBuffers(). This might save a few
* instructions when called from another translation unit, because it is
* specialized for nblocks == 1.
*/
bool
StartReadBuffer(ReadBuffersOperation *operation,
Buffer *buffer,
BlockNumber blocknum,
int flags)
{
int nblocks = 1;
bool result;
result = StartReadBuffersImpl(operation, buffer, blocknum, &nblocks, flags);
Assert(nblocks == 1); /* single block can't be short */
return result;
}
static inline bool
WaitReadBuffersCanStartIO(Buffer buffer, bool nowait)
{
if (BufferIsLocal(buffer))
{
BufferDesc *bufHdr = GetLocalBufferDescriptor(-buffer - 1);
return (pg_atomic_read_u32(&bufHdr->state) & BM_VALID) == 0;
}
else
return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait);
}
void
WaitReadBuffers(ReadBuffersOperation *operation)
{
Buffer *buffers;
int nblocks;
BlockNumber blocknum;
ForkNumber forknum;
IOContext io_context;
IOObject io_object;
char persistence;
/*
* Currently operations are only allowed to include a read of some range,
* with an optional extra buffer that is already pinned at the end. So
* nblocks can be at most one more than io_buffers_len.
*/
Assert((operation->nblocks == operation->io_buffers_len) ||
(operation->nblocks == operation->io_buffers_len + 1));
/* Find the range of the physical read we need to perform. */
nblocks = operation->io_buffers_len;
if (nblocks == 0)
return; /* nothing to do */
buffers = &operation->buffers[0];
blocknum = operation->blocknum;
forknum = operation->forknum;
persistence = operation->persistence;
if (persistence == RELPERSISTENCE_TEMP)
{
io_context = IOCONTEXT_NORMAL;
io_object = IOOBJECT_TEMP_RELATION;
}
else
{
io_context = IOContextForStrategy(operation->strategy);
io_object = IOOBJECT_RELATION;
}
/*
* We count all these blocks as read by this backend. This is traditional
* behavior, but might turn out to be not true if we find that someone
* else has beaten us and completed the read of some of these blocks. In
* that case the system globally double-counts, but we traditionally don't
* count this as a "hit", and we don't have a separate counter for "miss,
* but another backend completed the read".
*/
if (persistence == RELPERSISTENCE_TEMP)
pgBufferUsage.local_blks_read += nblocks;
else
pgBufferUsage.shared_blks_read += nblocks;
for (int i = 0; i < nblocks; ++i)
{
int io_buffers_len;
Buffer io_buffers[MAX_IO_COMBINE_LIMIT];
void *io_pages[MAX_IO_COMBINE_LIMIT];
instr_time io_start;
BlockNumber io_first_block;
/*
* Skip this block if someone else has already completed it. If an
* I/O is already in progress in another backend, this will wait for
* the outcome: either done, or something went wrong and we will
* retry.
*/
if (!WaitReadBuffersCanStartIO(buffers[i], false))
{
/*
* Report this as a 'hit' for this backend, even though it must
* have started out as a miss in PinBufferForBlock().
*/
TRACE_POSTGRESQL_BUFFER_READ_DONE(forknum, blocknum + i,
operation->smgr->smgr_rlocator.locator.spcOid,
operation->smgr->smgr_rlocator.locator.dbOid,
operation->smgr->smgr_rlocator.locator.relNumber,
operation->smgr->smgr_rlocator.backend,
true);
continue;
}
/* We found a buffer that we need to read in. */
io_buffers[0] = buffers[i];
io_pages[0] = BufferGetBlock(buffers[i]);
io_first_block = blocknum + i;
io_buffers_len = 1;
/*
* How many neighboring-on-disk blocks can we scatter-read into other
* buffers at the same time? In this case we don't wait if we see an
* I/O already in progress. We already hold BM_IO_IN_PROGRESS for the
* head block, so we should get on with that I/O as soon as possible.
* We'll come back to this block again, above.
*/
while ((i + 1) < nblocks &&
WaitReadBuffersCanStartIO(buffers[i + 1], true))
{
/* Must be consecutive block numbers. */
Assert(BufferGetBlockNumber(buffers[i + 1]) ==
BufferGetBlockNumber(buffers[i]) + 1);
io_buffers[io_buffers_len] = buffers[++i];
io_pages[io_buffers_len++] = BufferGetBlock(buffers[i]);
}
io_start = pgstat_prepare_io_time(track_io_timing);
smgrreadv(operation->smgr, forknum, io_first_block, io_pages, io_buffers_len);
pgstat_count_io_op_time(io_object, io_context, IOOP_READ, io_start,
io_buffers_len);
/* Verify each block we read, and terminate the I/O. */
for (int j = 0; j < io_buffers_len; ++j)
{
BufferDesc *bufHdr;
Block bufBlock;
if (persistence == RELPERSISTENCE_TEMP)
{
bufHdr = GetLocalBufferDescriptor(-io_buffers[j] - 1);
bufBlock = LocalBufHdrGetBlock(bufHdr);
}
else
{
bufHdr = GetBufferDescriptor(io_buffers[j] - 1);
bufBlock = BufHdrGetBlock(bufHdr);
}
/* check for garbage data */
if (!PageIsVerifiedExtended((Page) bufBlock, io_first_block + j,
PIV_LOG_WARNING | PIV_REPORT_STAT))
{
if ((operation->flags & READ_BUFFERS_ZERO_ON_ERROR) || zero_damaged_pages)
{
ereport(WARNING,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("invalid page in block %u of relation %s; zeroing out page",
io_first_block + j,
relpath(operation->smgr->smgr_rlocator, forknum))));
memset(bufBlock, 0, BLCKSZ);
}
else
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("invalid page in block %u of relation %s",
io_first_block + j,
relpath(operation->smgr->smgr_rlocator, forknum))));
}
/* Terminate I/O and set BM_VALID. */
if (persistence == RELPERSISTENCE_TEMP)
{
uint32 buf_state = pg_atomic_read_u32(&bufHdr->state);
buf_state |= BM_VALID;
pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
}
else
{
/* Set BM_VALID, terminate IO, and wake up any waiters */
TerminateBufferIO(bufHdr, false, BM_VALID, true);
}
/* Report I/Os as completing individually. */
TRACE_POSTGRESQL_BUFFER_READ_DONE(forknum, io_first_block + j,
operation->smgr->smgr_rlocator.locator.spcOid,
operation->smgr->smgr_rlocator.locator.dbOid,
operation->smgr->smgr_rlocator.locator.relNumber,
operation->smgr->smgr_rlocator.backend,
false);
}
if (VacuumCostActive)
VacuumCostBalance += VacuumCostPageMiss * io_buffers_len;
}
}
/*
* BufferAlloc -- subroutine for PinBufferForBlock. Handles lookup of a shared
* buffer. If no buffer exists already, selects a replacement victim and
* evicts the old page, but does NOT read in new page.
*
* "strategy" can be a buffer replacement strategy object, or NULL for
* the default strategy. The selected buffer's usage_count is advanced when
* using the default strategy, but otherwise possibly not (see PinBuffer).
*
* The returned buffer is pinned and is already marked as holding the
* desired page. If it already did have the desired page, *foundPtr is
* set true. Otherwise, *foundPtr is set false.
*
* io_context is passed as an output parameter to avoid calling
* IOContextForStrategy() when there is a shared buffers hit and no IO
* statistics need be captured.
*
* No locks are held either at entry or exit.
*/
static pg_attribute_always_inline BufferDesc *
BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
BlockNumber blockNum,
BufferAccessStrategy strategy,
bool *foundPtr, IOContext io_context)
{
BufferTag newTag; /* identity of requested block */
uint32 newHash; /* hash value for newTag */
LWLock *newPartitionLock; /* buffer partition lock for it */
int existing_buf_id;
Buffer victim_buffer;
BufferDesc *victim_buf_hdr;
uint32 victim_buf_state;
/* Make sure we will have room to remember the buffer pin */
ResourceOwnerEnlarge(CurrentResourceOwner);
ReservePrivateRefCountEntry();
/* create a tag so we can lookup the buffer */
InitBufferTag(&newTag, &smgr->smgr_rlocator.locator, forkNum, blockNum);
/* determine its hash code and partition lock ID */
newHash = BufTableHashCode(&newTag);
newPartitionLock = BufMappingPartitionLock(newHash);
/* see if the block is in the buffer pool already */
LWLockAcquire(newPartitionLock, LW_SHARED);
existing_buf_id = BufTableLookup(&newTag, newHash);
if (existing_buf_id >= 0)
{
BufferDesc *buf;
bool valid;
/*
* Found it. Now, pin the buffer so no one can steal it from the
* buffer pool, and check to see if the correct data has been loaded
* into the buffer.
*/
buf = GetBufferDescriptor(existing_buf_id);
valid = PinBuffer(buf, strategy);
/* Can release the mapping lock as soon as we've pinned it */
LWLockRelease(newPartitionLock);
*foundPtr = true;
if (!valid)
{
/*
* We can only get here if (a) someone else is still reading in
* the page, (b) a previous read attempt failed, or (c) someone
* called StartReadBuffers() but not yet WaitReadBuffers().
*/
*foundPtr = false;
}
return buf;
}
/*
* Didn't find it in the buffer pool. We'll have to initialize a new
* buffer. Remember to unlock the mapping lock while doing the work.
*/
LWLockRelease(newPartitionLock);
/*
* Acquire a victim buffer. Somebody else might try to do the same, we
* don't hold any conflicting locks. If so we'll have to undo our work
* later.
*/
victim_buffer = GetVictimBuffer(strategy, io_context);
victim_buf_hdr = GetBufferDescriptor(victim_buffer - 1);
/*
* Try to make a hashtable entry for the buffer under its new tag. If
* somebody else inserted another buffer for the tag, we'll release the
* victim buffer we acquired and use the already inserted one.
*/
LWLockAcquire(newPartitionLock, LW_EXCLUSIVE);
existing_buf_id = BufTableInsert(&newTag, newHash, victim_buf_hdr->buf_id);
if (existing_buf_id >= 0)
{
BufferDesc *existing_buf_hdr;
bool valid;
/*
* Got a collision. Someone has already done what we were about to do.
* We'll just handle this as if it were found in the buffer pool in
* the first place. First, give up the buffer we were planning to
* use.
*
* We could do this after releasing the partition lock, but then we'd
* have to call ResourceOwnerEnlarge() & ReservePrivateRefCountEntry()
* before acquiring the lock, for the rare case of such a collision.
*/
UnpinBuffer(victim_buf_hdr);
/*
* The victim buffer we acquired previously is clean and unused, let
* it be found again quickly
*/
StrategyFreeBuffer(victim_buf_hdr);
/* remaining code should match code at top of routine */
existing_buf_hdr = GetBufferDescriptor(existing_buf_id);
valid = PinBuffer(existing_buf_hdr, strategy);
/* Can release the mapping lock as soon as we've pinned it */
LWLockRelease(newPartitionLock);
*foundPtr = true;
if (!valid)
{
/*
* We can only get here if (a) someone else is still reading in
* the page, (b) a previous read attempt failed, or (c) someone
* called StartReadBuffers() but not yet WaitReadBuffers().
*/
*foundPtr = false;
}
return existing_buf_hdr;
}
/*
* Need to lock the buffer header too in order to change its tag.
*/
victim_buf_state = LockBufHdr(victim_buf_hdr);
/* some sanity checks while we hold the buffer header lock */
Assert(BUF_STATE_GET_REFCOUNT(victim_buf_state) == 1);
Assert(!(victim_buf_state & (BM_TAG_VALID | BM_VALID | BM_DIRTY | BM_IO_IN_PROGRESS)));
victim_buf_hdr->tag = newTag;
/*
* Make sure BM_PERMANENT is set for buffers that must be written at every
* checkpoint. Unlogged buffers only need to be written at shutdown
* checkpoints, except for their "init" forks, which need to be treated
* just like permanent relations.
*/
victim_buf_state |= BM_TAG_VALID | BUF_USAGECOUNT_ONE;
if (relpersistence == RELPERSISTENCE_PERMANENT || forkNum == INIT_FORKNUM)
victim_buf_state |= BM_PERMANENT;
UnlockBufHdr(victim_buf_hdr, victim_buf_state);
LWLockRelease(newPartitionLock);
/*
* Buffer contents are currently invalid.
*/
*foundPtr = false;
return victim_buf_hdr;
}
/*
* InvalidateBuffer -- mark a shared buffer invalid and return it to the
* freelist.
*
* The buffer header spinlock must be held at entry. We drop it before
* returning. (This is sane because the caller must have locked the
* buffer in order to be sure it should be dropped.)
*
* This is used only in contexts such as dropping a relation. We assume
* that no other backend could possibly be interested in using the page,
* so the only reason the buffer might be pinned is if someone else is
* trying to write it out. We have to let them finish before we can
* reclaim the buffer.
*
* The buffer could get reclaimed by someone else while we are waiting
* to acquire the necessary locks; if so, don't mess it up.
*/
static void
InvalidateBuffer(BufferDesc *buf)
{
BufferTag oldTag;
uint32 oldHash; /* hash value for oldTag */
LWLock *oldPartitionLock; /* buffer partition lock for it */
uint32 oldFlags;
uint32 buf_state;
/* Save the original buffer tag before dropping the spinlock */
oldTag = buf->tag;
buf_state = pg_atomic_read_u32(&buf->state);
Assert(buf_state & BM_LOCKED);
UnlockBufHdr(buf, buf_state);
/*
* Need to compute the old tag's hashcode and partition lock ID. XXX is it
* worth storing the hashcode in BufferDesc so we need not recompute it
* here? Probably not.
*/
oldHash = BufTableHashCode(&oldTag);
oldPartitionLock = BufMappingPartitionLock(oldHash);
retry:
/*
* Acquire exclusive mapping lock in preparation for changing the buffer's
* association.
*/
LWLockAcquire(oldPartitionLock, LW_EXCLUSIVE);
/* Re-lock the buffer header */
buf_state = LockBufHdr(buf);
/* If it's changed while we were waiting for lock, do nothing */
if (!BufferTagsEqual(&buf->tag, &oldTag))
{
UnlockBufHdr(buf, buf_state);
LWLockRelease(oldPartitionLock);
return;
}
/*
* We assume the only reason for it to be pinned is that someone else is
* flushing the page out. Wait for them to finish. (This could be an
* infinite loop if the refcount is messed up... it would be nice to time
* out after awhile, but there seems no way to be sure how many loops may
* be needed. Note that if the other guy has pinned the buffer but not
* yet done StartBufferIO, WaitIO will fall through and we'll effectively
* be busy-looping here.)
*/
if (BUF_STATE_GET_REFCOUNT(buf_state) != 0)
{
UnlockBufHdr(buf, buf_state);
LWLockRelease(oldPartitionLock);
/* safety check: should definitely not be our *own* pin */
if (GetPrivateRefCount(BufferDescriptorGetBuffer(buf)) > 0)
elog(ERROR, "buffer is pinned in InvalidateBuffer");
WaitIO(buf);
goto retry;
}
/*
* Clear out the buffer's tag and flags. We must do this to ensure that
* linear scans of the buffer array don't think the buffer is valid.
*/
oldFlags = buf_state & BUF_FLAG_MASK;
ClearBufferTag(&buf->tag);
buf_state &= ~(BUF_FLAG_MASK | BUF_USAGECOUNT_MASK);
UnlockBufHdr(buf, buf_state);
/*
* Remove the buffer from the lookup hashtable, if it was in there.
*/
if (oldFlags & BM_TAG_VALID)
BufTableDelete(&oldTag, oldHash);
/*
* Done with mapping lock.
*/
LWLockRelease(oldPartitionLock);
/*
* Insert the buffer at the head of the list of free buffers.
*/
StrategyFreeBuffer(buf);
}
/*
* Helper routine for GetVictimBuffer()
*
* Needs to be called on a buffer with a valid tag, pinned, but without the
* buffer header spinlock held.
*
* Returns true if the buffer can be reused, in which case the buffer is only
* pinned by this backend and marked as invalid, false otherwise.
*/
static bool
InvalidateVictimBuffer(BufferDesc *buf_hdr)
{
uint32 buf_state;
uint32 hash;
LWLock *partition_lock;
BufferTag tag;
Assert(GetPrivateRefCount(BufferDescriptorGetBuffer(buf_hdr)) == 1);
/* have buffer pinned, so it's safe to read tag without lock */
tag = buf_hdr->tag;
hash = BufTableHashCode(&tag);
partition_lock = BufMappingPartitionLock(hash);
LWLockAcquire(partition_lock, LW_EXCLUSIVE);
/* lock the buffer header */
buf_state = LockBufHdr(buf_hdr);
/*
* We have the buffer pinned nobody else should have been able to unset
* this concurrently.
*/
Assert(buf_state & BM_TAG_VALID);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
Assert(BufferTagsEqual(&buf_hdr->tag, &tag));
/*
* If somebody else pinned the buffer since, or even worse, dirtied it,
* give up on this buffer: It's clearly in use.
*/
if (BUF_STATE_GET_REFCOUNT(buf_state) != 1 || (buf_state & BM_DIRTY))
{
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
UnlockBufHdr(buf_hdr, buf_state);
LWLockRelease(partition_lock);
return false;
}
/*
* Clear out the buffer's tag and flags and usagecount. This is not
* strictly required, as BM_TAG_VALID/BM_VALID needs to be checked before
* doing anything with the buffer. But currently it's beneficial, as the
* cheaper pre-check for several linear scans of shared buffers use the
* tag (see e.g. FlushDatabaseBuffers()).
*/
ClearBufferTag(&buf_hdr->tag);
buf_state &= ~(BUF_FLAG_MASK | BUF_USAGECOUNT_MASK);
UnlockBufHdr(buf_hdr, buf_state);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
/* finally delete buffer from the buffer mapping table */
BufTableDelete(&tag, hash);
LWLockRelease(partition_lock);
Assert(!(buf_state & (BM_DIRTY | BM_VALID | BM_TAG_VALID)));
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
Assert(BUF_STATE_GET_REFCOUNT(pg_atomic_read_u32(&buf_hdr->state)) > 0);
return true;
}
static Buffer
GetVictimBuffer(BufferAccessStrategy strategy, IOContext io_context)
{
BufferDesc *buf_hdr;
Buffer buf;
uint32 buf_state;
bool from_ring;
/*
* Ensure, while the spinlock's not yet held, that there's a free refcount
* entry, and a resource owner slot for the pin.
*/
ReservePrivateRefCountEntry();
ResourceOwnerEnlarge(CurrentResourceOwner);
/* we return here if a prospective victim buffer gets used concurrently */
again:
/*
* Select a victim buffer. The buffer is returned with its header
* spinlock still held!
*/
buf_hdr = StrategyGetBuffer(strategy, &buf_state, &from_ring);
buf = BufferDescriptorGetBuffer(buf_hdr);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) == 0);
/* Pin the buffer and then release the buffer spinlock */
PinBuffer_Locked(buf_hdr);
/*
* We shouldn't have any other pins for this buffer.
*/
CheckBufferIsPinnedOnce(buf);
/*
* If the buffer was dirty, try to write it out. There is a race
* condition here, in that someone might dirty it after we released the
* buffer header lock above, or even while we are writing it out (since
* our share-lock won't prevent hint-bit updates). We will recheck the
* dirty bit after re-locking the buffer header.
*/
if (buf_state & BM_DIRTY)
{
LWLock *content_lock;
Assert(buf_state & BM_TAG_VALID);
Assert(buf_state & BM_VALID);
/*
* We need a share-lock on the buffer contents to write it out (else
* we might write invalid data, eg because someone else is compacting
* the page contents while we write). We must use a conditional lock
* acquisition here to avoid deadlock. Even though the buffer was not
* pinned (and therefore surely not locked) when StrategyGetBuffer
* returned it, someone else could have pinned and exclusive-locked it
* by the time we get here. If we try to get the lock unconditionally,
* we'd block waiting for them; if they later block waiting for us,
* deadlock ensues. (This has been observed to happen when two
* backends are both trying to split btree index pages, and the second
* one just happens to be trying to split the page the first one got
* from StrategyGetBuffer.)
*/
content_lock = BufferDescriptorGetContentLock(buf_hdr);
if (!LWLockConditionalAcquire(content_lock, LW_SHARED))
{
/*
* Someone else has locked the buffer, so give it up and loop back
* to get another one.
*/
UnpinBuffer(buf_hdr);
goto again;
}
/*
* If using a nondefault strategy, and writing the buffer would
* require a WAL flush, let the strategy decide whether to go ahead
* and write/reuse the buffer or to choose another victim. We need a
* lock to inspect the page LSN, so this can't be done inside
* StrategyGetBuffer.
*/
if (strategy != NULL)
{
XLogRecPtr lsn;
/* Read the LSN while holding buffer header lock */
buf_state = LockBufHdr(buf_hdr);
lsn = BufferGetLSN(buf_hdr);
UnlockBufHdr(buf_hdr, buf_state);
if (XLogNeedsFlush(lsn)
&& StrategyRejectBuffer(strategy, buf_hdr, from_ring))
{
LWLockRelease(content_lock);
UnpinBuffer(buf_hdr);
goto again;
}
}
/* OK, do the I/O */
FlushBuffer(buf_hdr, NULL, IOOBJECT_RELATION, io_context);
LWLockRelease(content_lock);
ScheduleBufferTagForWriteback(&BackendWritebackContext, io_context,
&buf_hdr->tag);
}
if (buf_state & BM_VALID)
{
/*
* When a BufferAccessStrategy is in use, blocks evicted from shared
* buffers are counted as IOOP_EVICT in the corresponding context
* (e.g. IOCONTEXT_BULKWRITE). Shared buffers are evicted by a
* strategy in two cases: 1) while initially claiming buffers for the
* strategy ring 2) to replace an existing strategy ring buffer
* because it is pinned or in use and cannot be reused.
*
* Blocks evicted from buffers already in the strategy ring are
* counted as IOOP_REUSE in the corresponding strategy context.
*
* At this point, we can accurately count evictions and reuses,
* because we have successfully claimed the valid buffer. Previously,
* we may have been forced to release the buffer due to concurrent
* pinners or erroring out.
*/
pgstat_count_io_op(IOOBJECT_RELATION, io_context,
from_ring ? IOOP_REUSE : IOOP_EVICT, 1);
}
/*
* If the buffer has an entry in the buffer mapping table, delete it. This
* can fail because another backend could have pinned or dirtied the
* buffer.
*/
if ((buf_state & BM_TAG_VALID) && !InvalidateVictimBuffer(buf_hdr))
{
UnpinBuffer(buf_hdr);
goto again;
}
/* a final set of sanity checks */
#ifdef USE_ASSERT_CHECKING
buf_state = pg_atomic_read_u32(&buf_hdr->state);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) == 1);
Assert(!(buf_state & (BM_TAG_VALID | BM_VALID | BM_DIRTY)));
CheckBufferIsPinnedOnce(buf);
#endif
return buf;
}
/*
* Limit the number of pins a batch operation may additionally acquire, to
* avoid running out of pinnable buffers.
*
* One additional pin is always allowed, as otherwise the operation likely
* cannot be performed at all.
*
* The number of allowed pins for a backend is computed based on
* shared_buffers and the maximum number of connections possible. That's very
* pessimistic, but outside of toy-sized shared_buffers it should allow
* sufficient pins.
*/
void
LimitAdditionalPins(uint32 *additional_pins)
{
uint32 max_backends;
int max_proportional_pins;
if (*additional_pins <= 1)
return;
max_backends = MaxBackends + NUM_AUXILIARY_PROCS;
max_proportional_pins = NBuffers / max_backends;
/*
* Subtract the approximate number of buffers already pinned by this
* backend. We get the number of "overflowed" pins for free, but don't
* know the number of pins in PrivateRefCountArray. The cost of
* calculating that exactly doesn't seem worth it, so just assume the max.
*/
max_proportional_pins -= PrivateRefCountOverflowed + REFCOUNT_ARRAY_ENTRIES;
if (max_proportional_pins <= 0)
max_proportional_pins = 1;
if (*additional_pins > max_proportional_pins)
*additional_pins = max_proportional_pins;
}
/*
* Logic shared between ExtendBufferedRelBy(), ExtendBufferedRelTo(). Just to
* avoid duplicating the tracing and relpersistence related logic.
*/
static BlockNumber
ExtendBufferedRelCommon(BufferManagerRelation bmr,
ForkNumber fork,
BufferAccessStrategy strategy,
uint32 flags,
uint32 extend_by,
BlockNumber extend_upto,
Buffer *buffers,
uint32 *extended_by)
{
BlockNumber first_block;
TRACE_POSTGRESQL_BUFFER_EXTEND_START(fork,
bmr.smgr->smgr_rlocator.locator.spcOid,
bmr.smgr->smgr_rlocator.locator.dbOid,
bmr.smgr->smgr_rlocator.locator.relNumber,
bmr.smgr->smgr_rlocator.backend,
extend_by);
if (bmr.relpersistence == RELPERSISTENCE_TEMP)
first_block = ExtendBufferedRelLocal(bmr, fork, flags,
extend_by, extend_upto,
buffers, &extend_by);
else
first_block = ExtendBufferedRelShared(bmr, fork, strategy, flags,
extend_by, extend_upto,
buffers, &extend_by);
*extended_by = extend_by;
TRACE_POSTGRESQL_BUFFER_EXTEND_DONE(fork,
bmr.smgr->smgr_rlocator.locator.spcOid,
bmr.smgr->smgr_rlocator.locator.dbOid,
bmr.smgr->smgr_rlocator.locator.relNumber,
bmr.smgr->smgr_rlocator.backend,
*extended_by,
first_block);
return first_block;
}
/*
* Implementation of ExtendBufferedRelBy() and ExtendBufferedRelTo() for
* shared buffers.
*/
static BlockNumber
ExtendBufferedRelShared(BufferManagerRelation bmr,
ForkNumber fork,
BufferAccessStrategy strategy,
uint32 flags,
uint32 extend_by,
BlockNumber extend_upto,
Buffer *buffers,
uint32 *extended_by)
{
BlockNumber first_block;
IOContext io_context = IOContextForStrategy(strategy);
instr_time io_start;
LimitAdditionalPins(&extend_by);
/*
* Acquire victim buffers for extension without holding extension lock.
* Writing out victim buffers is the most expensive part of extending the
* relation, particularly when doing so requires WAL flushes. Zeroing out
* the buffers is also quite expensive, so do that before holding the
* extension lock as well.
*
* These pages are pinned by us and not valid. While we hold the pin they
* can't be acquired as victim buffers by another backend.
*/
for (uint32 i = 0; i < extend_by; i++)
{
Block buf_block;
buffers[i] = GetVictimBuffer(strategy, io_context);
buf_block = BufHdrGetBlock(GetBufferDescriptor(buffers[i] - 1));
/* new buffers are zero-filled */
MemSet((char *) buf_block, 0, BLCKSZ);
}
/*
* Lock relation against concurrent extensions, unless requested not to.
*
* We use the same extension lock for all forks. That's unnecessarily
* restrictive, but currently extensions for forks don't happen often
* enough to make it worth locking more granularly.
*
* Note that another backend might have extended the relation by the time
* we get the lock.
*/
if (!(flags & EB_SKIP_EXTENSION_LOCK))
LockRelationForExtension(bmr.rel, ExclusiveLock);
/*
* If requested, invalidate size cache, so that smgrnblocks asks the
* kernel.
*/
if (flags & EB_CLEAR_SIZE_CACHE)
bmr.smgr->smgr_cached_nblocks[fork] = InvalidBlockNumber;
first_block = smgrnblocks(bmr.smgr, fork);
/*
* Now that we have the accurate relation size, check if the caller wants
* us to extend to only up to a specific size. If there were concurrent
* extensions, we might have acquired too many buffers and need to release
* them.
*/
if (extend_upto != InvalidBlockNumber)
{
uint32 orig_extend_by = extend_by;
if (first_block > extend_upto)
extend_by = 0;
else if ((uint64) first_block + extend_by > extend_upto)
extend_by = extend_upto - first_block;
for (uint32 i = extend_by; i < orig_extend_by; i++)
{
BufferDesc *buf_hdr = GetBufferDescriptor(buffers[i] - 1);
/*
* The victim buffer we acquired previously is clean and unused,
* let it be found again quickly
*/
StrategyFreeBuffer(buf_hdr);
UnpinBuffer(buf_hdr);
}
if (extend_by == 0)
{
if (!(flags & EB_SKIP_EXTENSION_LOCK))
UnlockRelationForExtension(bmr.rel, ExclusiveLock);
*extended_by = extend_by;
return first_block;
}
}
/* Fail if relation is already at maximum possible length */
if ((uint64) first_block + extend_by >= MaxBlockNumber)
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("cannot extend relation %s beyond %u blocks",
relpath(bmr.smgr->smgr_rlocator, fork),
MaxBlockNumber)));
/*
* Insert buffers into buffer table, mark as IO_IN_PROGRESS.
*
* This needs to happen before we extend the relation, because as soon as
* we do, other backends can start to read in those pages.
*/
for (uint32 i = 0; i < extend_by; i++)
{
Buffer victim_buf = buffers[i];
BufferDesc *victim_buf_hdr = GetBufferDescriptor(victim_buf - 1);
BufferTag tag;
uint32 hash;
LWLock *partition_lock;
int existing_id;
/* in case we need to pin an existing buffer below */
ResourceOwnerEnlarge(CurrentResourceOwner);
ReservePrivateRefCountEntry();
InitBufferTag(&tag, &bmr.smgr->smgr_rlocator.locator, fork, first_block + i);
hash = BufTableHashCode(&tag);
partition_lock = BufMappingPartitionLock(hash);
LWLockAcquire(partition_lock, LW_EXCLUSIVE);
existing_id = BufTableInsert(&tag, hash, victim_buf_hdr->buf_id);
/*
* We get here only in the corner case where we are trying to extend
* the relation but we found a pre-existing buffer. This can happen
* because a prior attempt at extending the relation failed, and
* because mdread doesn't complain about reads beyond EOF (when
* zero_damaged_pages is ON) and so a previous attempt to read a block
* beyond EOF could have left a "valid" zero-filled buffer.
* Unfortunately, we have also seen this case occurring because of
* buggy Linux kernels that sometimes return an lseek(SEEK_END) result
* that doesn't account for a recent write. In that situation, the
* pre-existing buffer would contain valid data that we don't want to
* overwrite. Since the legitimate cases should always have left a
* zero-filled buffer, complain if not PageIsNew.
*/
if (existing_id >= 0)
{
BufferDesc *existing_hdr = GetBufferDescriptor(existing_id);
Block buf_block;
bool valid;
/*
* Pin the existing buffer before releasing the partition lock,
* preventing it from being evicted.
*/
valid = PinBuffer(existing_hdr, strategy);
LWLockRelease(partition_lock);
/*
* The victim buffer we acquired previously is clean and unused,
* let it be found again quickly
*/
StrategyFreeBuffer(victim_buf_hdr);
UnpinBuffer(victim_buf_hdr);
buffers[i] = BufferDescriptorGetBuffer(existing_hdr);
buf_block = BufHdrGetBlock(existing_hdr);
if (valid && !PageIsNew((Page) buf_block))
ereport(ERROR,
(errmsg("unexpected data beyond EOF in block %u of relation %s",
existing_hdr->tag.blockNum, relpath(bmr.smgr->smgr_rlocator, fork)),
errhint("This has been seen to occur with buggy kernels; consider updating your system.")));
/*
* We *must* do smgr[zero]extend before succeeding, else the page
* will not be reserved by the kernel, and the next P_NEW call
* will decide to return the same page. Clear the BM_VALID bit,
* do StartBufferIO() and proceed.
*
* Loop to handle the very small possibility that someone re-sets
* BM_VALID between our clearing it and StartBufferIO inspecting
* it.
*/
do
{
uint32 buf_state = LockBufHdr(existing_hdr);
buf_state &= ~BM_VALID;
UnlockBufHdr(existing_hdr, buf_state);
} while (!StartBufferIO(existing_hdr, true, false));
}
else
{
uint32 buf_state;
buf_state = LockBufHdr(victim_buf_hdr);
/* some sanity checks while we hold the buffer header lock */
Assert(!(buf_state & (BM_VALID | BM_TAG_VALID | BM_DIRTY | BM_JUST_DIRTIED)));
Assert(BUF_STATE_GET_REFCOUNT(buf_state) == 1);
victim_buf_hdr->tag = tag;
buf_state |= BM_TAG_VALID | BUF_USAGECOUNT_ONE;
if (bmr.relpersistence == RELPERSISTENCE_PERMANENT || fork == INIT_FORKNUM)
buf_state |= BM_PERMANENT;
UnlockBufHdr(victim_buf_hdr, buf_state);
LWLockRelease(partition_lock);
/* XXX: could combine the locked operations in it with the above */
StartBufferIO(victim_buf_hdr, true, false);
}
}
io_start = pgstat_prepare_io_time(track_io_timing);
/*
* Note: if smgrzeroextend fails, we will end up with buffers that are
* allocated but not marked BM_VALID. The next relation extension will
* still select the same block number (because the relation didn't get any
* longer on disk) and so future attempts to extend the relation will find
* the same buffers (if they have not been recycled) but come right back
* here to try smgrzeroextend again.
*
* We don't need to set checksum for all-zero pages.
*/
smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
/*
* Release the file-extension lock; it's now OK for someone else to extend
* the relation some more.
*
* We remove IO_IN_PROGRESS after this, as waking up waiting backends can
* take noticeable time.
*/
if (!(flags & EB_SKIP_EXTENSION_LOCK))
UnlockRelationForExtension(bmr.rel, ExclusiveLock);
pgstat_count_io_op_time(IOOBJECT_RELATION, io_context, IOOP_EXTEND,
io_start, extend_by);
/* Set BM_VALID, terminate IO, and wake up any waiters */
for (uint32 i = 0; i < extend_by; i++)
{
Buffer buf = buffers[i];
BufferDesc *buf_hdr = GetBufferDescriptor(buf - 1);
bool lock = false;
if (flags & EB_LOCK_FIRST && i == 0)
lock = true;
else if (flags & EB_LOCK_TARGET)
{
Assert(extend_upto != InvalidBlockNumber);
if (first_block + i + 1 == extend_upto)
lock = true;
}
if (lock)
LWLockAcquire(BufferDescriptorGetContentLock(buf_hdr), LW_EXCLUSIVE);
TerminateBufferIO(buf_hdr, false, BM_VALID, true);
}
pgBufferUsage.shared_blks_written += extend_by;
*extended_by = extend_by;
return first_block;
}
/*
* BufferIsExclusiveLocked
*
* Checks if buffer is exclusive-locked.
*
* Buffer must be pinned.
*/
bool
BufferIsExclusiveLocked(Buffer buffer)
{
BufferDesc *bufHdr;
if (BufferIsLocal(buffer))
{
int bufid = -buffer - 1;
bufHdr = GetLocalBufferDescriptor(bufid);
}
else
{
bufHdr = GetBufferDescriptor(buffer - 1);
}
Assert(BufferIsPinned(buffer));
return LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
LW_EXCLUSIVE);
}
/*
* BufferIsDirty
*
* Checks if buffer is already dirty.
*
* Buffer must be pinned and exclusive-locked. (Without an exclusive lock,
* the result may be stale before it's returned.)
*/
bool
BufferIsDirty(Buffer buffer)
{
BufferDesc *bufHdr;
if (BufferIsLocal(buffer))
{
int bufid = -buffer - 1;
bufHdr = GetLocalBufferDescriptor(bufid);
}
else
{
bufHdr = GetBufferDescriptor(buffer - 1);
}
Assert(BufferIsPinned(buffer));
Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
LW_EXCLUSIVE));
return pg_atomic_read_u32(&bufHdr->state) & BM_DIRTY;
}
/*
* MarkBufferDirty
*
* Marks buffer contents as dirty (actual write happens later).
*
* Buffer must be pinned and exclusive-locked. (If caller does not hold
* exclusive lock, then somebody could be in process of writing the buffer,
* leading to risk of bad data written to disk.)
*/
void
MarkBufferDirty(Buffer buffer)
{
BufferDesc *bufHdr;
uint32 buf_state;
uint32 old_buf_state;
if (!BufferIsValid(buffer))
elog(ERROR, "bad buffer ID: %d", buffer);
if (BufferIsLocal(buffer))
{
MarkLocalBufferDirty(buffer);
return;
}
bufHdr = GetBufferDescriptor(buffer - 1);
Assert(BufferIsPinned(buffer));
Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
LW_EXCLUSIVE));
old_buf_state = pg_atomic_read_u32(&bufHdr->state);
for (;;)
{
if (old_buf_state & BM_LOCKED)
old_buf_state = WaitBufHdrUnlocked(bufHdr);
buf_state = old_buf_state;
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
buf_state |= BM_DIRTY | BM_JUST_DIRTIED;
if (pg_atomic_compare_exchange_u32(&bufHdr->state, &old_buf_state,
buf_state))
break;
}
/*
* If the buffer was not dirty already, do vacuum accounting.
*/
if (!(old_buf_state & BM_DIRTY))
{
pgBufferUsage.shared_blks_dirtied++;
if (VacuumCostActive)
VacuumCostBalance += VacuumCostPageDirty;
}
}
/*
* ReleaseAndReadBuffer -- combine ReleaseBuffer() and ReadBuffer()
*
* Formerly, this saved one cycle of acquiring/releasing the BufMgrLock
* compared to calling the two routines separately. Now it's mainly just
* a convenience function. However, if the passed buffer is valid and
* already contains the desired block, we just return it as-is; and that
* does save considerable work compared to a full release and reacquire.
*
* Note: it is OK to pass buffer == InvalidBuffer, indicating that no old
* buffer actually needs to be released. This case is the same as ReadBuffer,
* but can save some tests in the caller.
*/
Buffer
ReleaseAndReadBuffer(Buffer buffer,
Relation relation,
BlockNumber blockNum)
{
ForkNumber forkNum = MAIN_FORKNUM;
BufferDesc *bufHdr;
if (BufferIsValid(buffer))
{
Assert(BufferIsPinned(buffer));
if (BufferIsLocal(buffer))
{
bufHdr = GetLocalBufferDescriptor(-buffer - 1);
if (bufHdr->tag.blockNum == blockNum &&
BufTagMatchesRelFileLocator(&bufHdr->tag, &relation->rd_locator) &&
BufTagGetForkNum(&bufHdr->tag) == forkNum)
return buffer;
UnpinLocalBuffer(buffer);
}
else
{
bufHdr = GetBufferDescriptor(buffer - 1);
/* we have pin, so it's ok to examine tag without spinlock */
if (bufHdr->tag.blockNum == blockNum &&
BufTagMatchesRelFileLocator(&bufHdr->tag, &relation->rd_locator) &&
BufTagGetForkNum(&bufHdr->tag) == forkNum)
return buffer;
UnpinBuffer(bufHdr);
}
}
return ReadBuffer(relation, blockNum);
}
/*
* PinBuffer -- make buffer unavailable for replacement.
*
* For the default access strategy, the buffer's usage_count is incremented
* when we first pin it; for other strategies we just make sure the usage_count
* isn't zero. (The idea of the latter is that we don't want synchronized
* heap scans to inflate the count, but we need it to not be zero to discourage
* other backends from stealing buffers from our ring. As long as we cycle
* through the ring faster than the global clock-sweep cycles, buffers in
* our ring won't be chosen as victims for replacement by other backends.)
*
* This should be applied only to shared buffers, never local ones.
*
* Since buffers are pinned/unpinned very frequently, pin buffers without
* taking the buffer header lock; instead update the state variable in loop of
* CAS operations. Hopefully it's just a single CAS.
*
* Note that ResourceOwnerEnlarge() and ReservePrivateRefCountEntry()
* must have been done already.
*
* Returns true if buffer is BM_VALID, else false. This provision allows
* some callers to avoid an extra spinlock cycle.
*/
static bool
PinBuffer(BufferDesc *buf, BufferAccessStrategy strategy)
{
Buffer b = BufferDescriptorGetBuffer(buf);
bool result;
PrivateRefCountEntry *ref;
Assert(!BufferIsLocal(b));
Assert(ReservedRefCountEntry != NULL);
ref = GetPrivateRefCountEntry(b, true);
if (ref == NULL)
{
uint32 buf_state;
uint32 old_buf_state;
ref = NewPrivateRefCountEntry(b);
old_buf_state = pg_atomic_read_u32(&buf->state);
for (;;)
{
if (old_buf_state & BM_LOCKED)
old_buf_state = WaitBufHdrUnlocked(buf);
buf_state = old_buf_state;
/* increase refcount */
buf_state += BUF_REFCOUNT_ONE;
if (strategy == NULL)
{
/* Default case: increase usagecount unless already max. */
if (BUF_STATE_GET_USAGECOUNT(buf_state) < BM_MAX_USAGE_COUNT)
buf_state += BUF_USAGECOUNT_ONE;
}
else
{
/*
* Ring buffers shouldn't evict others from pool. Thus we
* don't make usagecount more than 1.
*/
if (BUF_STATE_GET_USAGECOUNT(buf_state) == 0)
buf_state += BUF_USAGECOUNT_ONE;
}
if (pg_atomic_compare_exchange_u32(&buf->state, &old_buf_state,
buf_state))
{
result = (buf_state & BM_VALID) != 0;
/*
* Assume that we acquired a buffer pin for the purposes of
* Valgrind buffer client checks (even in !result case) to
* keep things simple. Buffers that are unsafe to access are
* not generally guaranteed to be marked undefined or
* non-accessible in any case.
*/
VALGRIND_MAKE_MEM_DEFINED(BufHdrGetBlock(buf), BLCKSZ);
break;
}
}
}
else
{
/*
* If we previously pinned the buffer, it is likely to be valid, but
* it may not be if StartReadBuffers() was called and
* WaitReadBuffers() hasn't been called yet. We'll check by loading
* the flags without locking. This is racy, but it's OK to return
* false spuriously: when WaitReadBuffers() calls StartBufferIO(),
* it'll see that it's now valid.
*
* Note: We deliberately avoid a Valgrind client request here.
* Individual access methods can optionally superimpose buffer page
* client requests on top of our client requests to enforce that
* buffers are only accessed while locked (and pinned). It's possible
* that the buffer page is legitimately non-accessible here. We
* cannot meddle with that.
*/
result = (pg_atomic_read_u32(&buf->state) & BM_VALID) != 0;
}
ref->refcount++;
Assert(ref->refcount > 0);
ResourceOwnerRememberBuffer(CurrentResourceOwner, b);
return result;
}
/*
* PinBuffer_Locked -- as above, but caller already locked the buffer header.
* The spinlock is released before return.
*
* As this function is called with the spinlock held, the caller has to
* previously call ReservePrivateRefCountEntry() and
* ResourceOwnerEnlarge(CurrentResourceOwner);
*
* Currently, no callers of this function want to modify the buffer's
* usage_count at all, so there's no need for a strategy parameter.
* Also we don't bother with a BM_VALID test (the caller could check that for
* itself).
*
* Also all callers only ever use this function when it's known that the
* buffer can't have a preexisting pin by this backend. That allows us to skip
* searching the private refcount array & hash, which is a boon, because the
* spinlock is still held.
*
* Note: use of this routine is frequently mandatory, not just an optimization
* to save a spin lock/unlock cycle, because we need to pin a buffer before
* its state can change under us.
*/
static void
PinBuffer_Locked(BufferDesc *buf)
{
Buffer b;
PrivateRefCountEntry *ref;
uint32 buf_state;
/*
* As explained, We don't expect any preexisting pins. That allows us to
* manipulate the PrivateRefCount after releasing the spinlock
*/
Assert(GetPrivateRefCountEntry(BufferDescriptorGetBuffer(buf), false) == NULL);
/*
* Buffer can't have a preexisting pin, so mark its page as defined to
* Valgrind (this is similar to the PinBuffer() case where the backend
* doesn't already have a buffer pin)
*/
VALGRIND_MAKE_MEM_DEFINED(BufHdrGetBlock(buf), BLCKSZ);
/*
* Since we hold the buffer spinlock, we can update the buffer state and
* release the lock in one operation.
*/
buf_state = pg_atomic_read_u32(&buf->state);
Assert(buf_state & BM_LOCKED);
buf_state += BUF_REFCOUNT_ONE;
UnlockBufHdr(buf, buf_state);
b = BufferDescriptorGetBuffer(buf);
ref = NewPrivateRefCountEntry(b);
ref->refcount++;
ResourceOwnerRememberBuffer(CurrentResourceOwner, b);
}
/*
* UnpinBuffer -- make buffer available for replacement.
*
* This should be applied only to shared buffers, never local ones. This
* always adjusts CurrentResourceOwner.
*/
static void
UnpinBuffer(BufferDesc *buf)
{
Buffer b = BufferDescriptorGetBuffer(buf);
ResourceOwnerForgetBuffer(CurrentResourceOwner, b);
UnpinBufferNoOwner(buf);
}
static void
UnpinBufferNoOwner(BufferDesc *buf)
{
PrivateRefCountEntry *ref;
Buffer b = BufferDescriptorGetBuffer(buf);
Assert(!BufferIsLocal(b));
/* not moving as we're likely deleting it soon anyway */
ref = GetPrivateRefCountEntry(b, false);
Assert(ref != NULL);
Assert(ref->refcount > 0);
ref->refcount--;
if (ref->refcount == 0)
{
uint32 buf_state;
uint32 old_buf_state;
/*
* Mark buffer non-accessible to Valgrind.
*
* Note that the buffer may have already been marked non-accessible
* within access method code that enforces that buffers are only
* accessed while a buffer lock is held.
*/
VALGRIND_MAKE_MEM_NOACCESS(BufHdrGetBlock(buf), BLCKSZ);
/* I'd better not still hold the buffer content lock */
Assert(!LWLockHeldByMe(BufferDescriptorGetContentLock(buf)));
/*
* Decrement the shared reference count.
*
* Since buffer spinlock holder can update status using just write,
* it's not safe to use atomic decrement here; thus use a CAS loop.
*/
old_buf_state = pg_atomic_read_u32(&buf->state);
for (;;)
{
if (old_buf_state & BM_LOCKED)
old_buf_state = WaitBufHdrUnlocked(buf);
buf_state = old_buf_state;
buf_state -= BUF_REFCOUNT_ONE;
if (pg_atomic_compare_exchange_u32(&buf->state, &old_buf_state,
buf_state))
break;
}
/* Support LockBufferForCleanup() */
if (buf_state & BM_PIN_COUNT_WAITER)
{
/*
* Acquire the buffer header lock, re-check that there's a waiter.
* Another backend could have unpinned this buffer, and already
* woken up the waiter. There's no danger of the buffer being
* replaced after we unpinned it above, as it's pinned by the
* waiter.
*/
buf_state = LockBufHdr(buf);
if ((buf_state & BM_PIN_COUNT_WAITER) &&
BUF_STATE_GET_REFCOUNT(buf_state) == 1)
{
/* we just released the last pin other than the waiter's */
int wait_backend_pgprocno = buf->wait_backend_pgprocno;
buf_state &= ~BM_PIN_COUNT_WAITER;
UnlockBufHdr(buf, buf_state);
ProcSendSignal(wait_backend_pgprocno);
}
else
UnlockBufHdr(buf, buf_state);
}
ForgetPrivateRefCountEntry(ref);
}
}
#define ST_SORT sort_checkpoint_bufferids
#define ST_ELEMENT_TYPE CkptSortItem
#define ST_COMPARE(a, b) ckpt_buforder_comparator(a, b)
#define ST_SCOPE static
#define ST_DEFINE
#include <lib/sort_template.h>
/*
* BufferSync -- Write out all dirty buffers in the pool.
*
* This is called at checkpoint time to write out all dirty shared buffers.
* The checkpoint request flags should be passed in. If CHECKPOINT_IMMEDIATE
* is set, we disable delays between writes; if CHECKPOINT_IS_SHUTDOWN,
* CHECKPOINT_END_OF_RECOVERY or CHECKPOINT_FLUSH_ALL is set, we write even
* unlogged buffers, which are otherwise skipped. The remaining flags
* currently have no effect here.
*/
static void
BufferSync(int flags)
{
uint32 buf_state;
int buf_id;
int num_to_scan;
int num_spaces;
int num_processed;
int num_written;
CkptTsStatus *per_ts_stat = NULL;
Oid last_tsid;
binaryheap *ts_heap;
int i;
int mask = BM_DIRTY;
WritebackContext wb_context;
/*
* Unless this is a shutdown checkpoint or we have been explicitly told,
* we write only permanent, dirty buffers. But at shutdown or end of
* recovery, we write all dirty buffers.
*/
if (!((flags & (CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_END_OF_RECOVERY |
CHECKPOINT_FLUSH_ALL))))
mask |= BM_PERMANENT;
/*
* Loop over all buffers, and mark the ones that need to be written with
* BM_CHECKPOINT_NEEDED. Count them as we go (num_to_scan), so that we
* can estimate how much work needs to be done.
*
* This allows us to write only those pages that were dirty when the
* checkpoint began, and not those that get dirtied while it proceeds.
* Whenever a page with BM_CHECKPOINT_NEEDED is written out, either by us
* later in this function, or by normal backends or the bgwriter cleaning
* scan, the flag is cleared. Any buffer dirtied after this point won't
* have the flag set.
*
* Note that if we fail to write some buffer, we may leave buffers with
* BM_CHECKPOINT_NEEDED still set. This is OK since any such buffer would
* certainly need to be written for the next checkpoint attempt, too.
*/
num_to_scan = 0;
for (buf_id = 0; buf_id < NBuffers; buf_id++)
{
BufferDesc *bufHdr = GetBufferDescriptor(buf_id);
/*
* Header spinlock is enough to examine BM_DIRTY, see comment in
* SyncOneBuffer.
*/
buf_state = LockBufHdr(bufHdr);
if ((buf_state & mask) == mask)
{
CkptSortItem *item;
buf_state |= BM_CHECKPOINT_NEEDED;
item = &CkptBufferIds[num_to_scan++];
item->buf_id = buf_id;
item->tsId = bufHdr->tag.spcOid;
item->relNumber = BufTagGetRelNumber(&bufHdr->tag);
item->forkNum = BufTagGetForkNum(&bufHdr->tag);
item->blockNum = bufHdr->tag.blockNum;
}
UnlockBufHdr(bufHdr, buf_state);
/* Check for barrier events in case NBuffers is large. */
if (ProcSignalBarrierPending)
ProcessProcSignalBarrier();
}
if (num_to_scan == 0)
return; /* nothing to do */
WritebackContextInit(&wb_context, &checkpoint_flush_after);
TRACE_POSTGRESQL_BUFFER_SYNC_START(NBuffers, num_to_scan);
/*
* Sort buffers that need to be written to reduce the likelihood of random
* IO. The sorting is also important for the implementation of balancing
* writes between tablespaces. Without balancing writes we'd potentially
* end up writing to the tablespaces one-by-one; possibly overloading the
* underlying system.
*/
sort_checkpoint_bufferids(CkptBufferIds, num_to_scan);
num_spaces = 0;
/*
* Allocate progress status for each tablespace with buffers that need to
* be flushed. This requires the to-be-flushed array to be sorted.
*/
last_tsid = InvalidOid;
for (i = 0; i < num_to_scan; i++)
{
CkptTsStatus *s;
Oid cur_tsid;
cur_tsid = CkptBufferIds[i].tsId;
/*
* Grow array of per-tablespace status structs, every time a new
* tablespace is found.
*/
if (last_tsid == InvalidOid || last_tsid != cur_tsid)
{
Size sz;
num_spaces++;
/*
* Not worth adding grow-by-power-of-2 logic here - even with a
* few hundred tablespaces this should be fine.
*/
sz = sizeof(CkptTsStatus) * num_spaces;
if (per_ts_stat == NULL)
per_ts_stat = (CkptTsStatus *) palloc(sz);
else
per_ts_stat = (CkptTsStatus *) repalloc(per_ts_stat, sz);
s = &per_ts_stat[num_spaces - 1];
memset(s, 0, sizeof(*s));
s->tsId = cur_tsid;
/*
* The first buffer in this tablespace. As CkptBufferIds is sorted
* by tablespace all (s->num_to_scan) buffers in this tablespace
* will follow afterwards.
*/
s->index = i;
/*
* progress_slice will be determined once we know how many buffers
* are in each tablespace, i.e. after this loop.
*/
last_tsid = cur_tsid;
}
else
{
s = &per_ts_stat[num_spaces - 1];
}
s->num_to_scan++;
/* Check for barrier events. */
if (ProcSignalBarrierPending)
ProcessProcSignalBarrier();
}
Assert(num_spaces > 0);
/*
* Build a min-heap over the write-progress in the individual tablespaces,
* and compute how large a portion of the total progress a single
* processed buffer is.
*/
ts_heap = binaryheap_allocate(num_spaces,
ts_ckpt_progress_comparator,
NULL);
for (i = 0; i < num_spaces; i++)
{
CkptTsStatus *ts_stat = &per_ts_stat[i];
ts_stat->progress_slice = (float8) num_to_scan / ts_stat->num_to_scan;
binaryheap_add_unordered(ts_heap, PointerGetDatum(ts_stat));
}
binaryheap_build(ts_heap);
/*
* Iterate through to-be-checkpointed buffers and write the ones (still)
* marked with BM_CHECKPOINT_NEEDED. The writes are balanced between
* tablespaces; otherwise the sorting would lead to only one tablespace
* receiving writes at a time, making inefficient use of the hardware.
*/
num_processed = 0;
num_written = 0;
while (!binaryheap_empty(ts_heap))
{
BufferDesc *bufHdr = NULL;
CkptTsStatus *ts_stat = (CkptTsStatus *)
DatumGetPointer(binaryheap_first(ts_heap));
buf_id = CkptBufferIds[ts_stat->index].buf_id;
Assert(buf_id != -1);
bufHdr = GetBufferDescriptor(buf_id);
num_processed++;
/*
* We don't need to acquire the lock here, because we're only looking
* at a single bit. It's possible that someone else writes the buffer
* and clears the flag right after we check, but that doesn't matter
* since SyncOneBuffer will then do nothing. However, there is a
* further race condition: it's conceivable that between the time we
* examine the bit here and the time SyncOneBuffer acquires the lock,
* someone else not only wrote the buffer but replaced it with another
* page and dirtied it. In that improbable case, SyncOneBuffer will
* write the buffer though we didn't need to. It doesn't seem worth
* guarding against this, though.
*/
if (pg_atomic_read_u32(&bufHdr->state) & BM_CHECKPOINT_NEEDED)
{
if (SyncOneBuffer(buf_id, false, &wb_context) & BUF_WRITTEN)
{
TRACE_POSTGRESQL_BUFFER_SYNC_WRITTEN(buf_id);
PendingCheckpointerStats.buffers_written++;
num_written++;
}
}
/*
* Measure progress independent of actually having to flush the buffer
* - otherwise writing become unbalanced.
*/
ts_stat->progress += ts_stat->progress_slice;
ts_stat->num_scanned++;
ts_stat->index++;
/* Have all the buffers from the tablespace been processed? */
if (ts_stat->num_scanned == ts_stat->num_to_scan)
{
binaryheap_remove_first(ts_heap);
}
else
{
/* update heap with the new progress */
binaryheap_replace_first(ts_heap, PointerGetDatum(ts_stat));
}
/*
* Sleep to throttle our I/O rate.
*
* (This will check for barrier events even if it doesn't sleep.)
*/
CheckpointWriteDelay(flags, (double) num_processed / num_to_scan);
}
/*
* Issue all pending flushes. Only checkpointer calls BufferSync(), so
* IOContext will always be IOCONTEXT_NORMAL.
*/
IssuePendingWritebacks(&wb_context, IOCONTEXT_NORMAL);
pfree(per_ts_stat);
per_ts_stat = NULL;
binaryheap_free(ts_heap);
/*
* Update checkpoint statistics. As noted above, this doesn't include
* buffers written by other backends or bgwriter scan.
*/
CheckpointStats.ckpt_bufs_written += num_written;
TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_scan);
}
/*
* BgBufferSync -- Write out some dirty buffers in the pool.
*
* This is called periodically by the background writer process.
*
* Returns true if it's appropriate for the bgwriter process to go into
* low-power hibernation mode. (This happens if the strategy clock sweep
* has been "lapped" and no buffer allocations have occurred recently,
* or if the bgwriter has been effectively disabled by setting
* bgwriter_lru_maxpages to 0.)
*/
bool
BgBufferSync(WritebackContext *wb_context)
{
/* info obtained from freelist.c */
int strategy_buf_id;
uint32 strategy_passes;
uint32 recent_alloc;
/*
* Information saved between calls so we can determine the strategy
* point's advance rate and avoid scanning already-cleaned buffers.
*/
static bool saved_info_valid = false;
static int prev_strategy_buf_id;
static uint32 prev_strategy_passes;
static int next_to_clean;
static uint32 next_passes;
/* Moving averages of allocation rate and clean-buffer density */
static float smoothed_alloc = 0;
static float smoothed_density = 10.0;
/* Potentially these could be tunables, but for now, not */
float smoothing_samples = 16;
float scan_whole_pool_milliseconds = 120000.0;
/* Used to compute how far we scan ahead */
long strategy_delta;
int bufs_to_lap;
int bufs_ahead;
float scans_per_alloc;
int reusable_buffers_est;
int upcoming_alloc_est;
int min_scan_buffers;
/* Variables for the scanning loop proper */
int num_to_scan;
int num_written;
int reusable_buffers;
/* Variables for final smoothed_density update */
long new_strategy_delta;
uint32 new_recent_alloc;
/*
* Find out where the freelist clock sweep currently is, and how many
* buffer allocations have happened since our last call.
*/
strategy_buf_id = StrategySyncStart(&strategy_passes, &recent_alloc);
/* Report buffer alloc counts to pgstat */
PendingBgWriterStats.buf_alloc += recent_alloc;
/*
* If we're not running the LRU scan, just stop after doing the stats
* stuff. We mark the saved state invalid so that we can recover sanely
* if LRU scan is turned back on later.
*/
if (bgwriter_lru_maxpages <= 0)
{
saved_info_valid = false;
return true;
}
/*
* Compute strategy_delta = how many buffers have been scanned by the
* clock sweep since last time. If first time through, assume none. Then
* see if we are still ahead of the clock sweep, and if so, how many
* buffers we could scan before we'd catch up with it and "lap" it. Note:
* weird-looking coding of xxx_passes comparisons are to avoid bogus
* behavior when the passes counts wrap around.
*/
if (saved_info_valid)
{
int32 passes_delta = strategy_passes - prev_strategy_passes;
strategy_delta = strategy_buf_id - prev_strategy_buf_id;
strategy_delta += (long) passes_delta * NBuffers;
Assert(strategy_delta >= 0);
if ((int32) (next_passes - strategy_passes) > 0)
{
/* we're one pass ahead of the strategy point */
bufs_to_lap = strategy_buf_id - next_to_clean;
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter ahead: bgw %u-%u strategy %u-%u delta=%ld lap=%d",
next_passes, next_to_clean,
strategy_passes, strategy_buf_id,
strategy_delta, bufs_to_lap);
#endif
}
else if (next_passes == strategy_passes &&
next_to_clean >= strategy_buf_id)
{
/* on same pass, but ahead or at least not behind */
bufs_to_lap = NBuffers - (next_to_clean - strategy_buf_id);
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter ahead: bgw %u-%u strategy %u-%u delta=%ld lap=%d",
next_passes, next_to_clean,
strategy_passes, strategy_buf_id,
strategy_delta, bufs_to_lap);
#endif
}
else
{
/*
* We're behind, so skip forward to the strategy point and start
* cleaning from there.
*/
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter behind: bgw %u-%u strategy %u-%u delta=%ld",
next_passes, next_to_clean,
strategy_passes, strategy_buf_id,
strategy_delta);
#endif
next_to_clean = strategy_buf_id;
next_passes = strategy_passes;
bufs_to_lap = NBuffers;
}
}
else
{
/*
* Initializing at startup or after LRU scanning had been off. Always
* start at the strategy point.
*/
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter initializing: strategy %u-%u",
strategy_passes, strategy_buf_id);
#endif
strategy_delta = 0;
next_to_clean = strategy_buf_id;
next_passes = strategy_passes;
bufs_to_lap = NBuffers;
}
/* Update saved info for next time */
prev_strategy_buf_id = strategy_buf_id;
prev_strategy_passes = strategy_passes;
saved_info_valid = true;
/*
* Compute how many buffers had to be scanned for each new allocation, ie,
* 1/density of reusable buffers, and track a moving average of that.
*
* If the strategy point didn't move, we don't update the density estimate
*/
if (strategy_delta > 0 && recent_alloc > 0)
{
scans_per_alloc = (float) strategy_delta / (float) recent_alloc;
smoothed_density += (scans_per_alloc - smoothed_density) /
smoothing_samples;
}
/*
* Estimate how many reusable buffers there are between the current
* strategy point and where we've scanned ahead to, based on the smoothed
* density estimate.
*/
bufs_ahead = NBuffers - bufs_to_lap;
reusable_buffers_est = (float) bufs_ahead / smoothed_density;
/*
* Track a moving average of recent buffer allocations. Here, rather than
* a true average we want a fast-attack, slow-decline behavior: we
* immediately follow any increase.
*/
if (smoothed_alloc <= (float) recent_alloc)
smoothed_alloc = recent_alloc;
else
smoothed_alloc += ((float) recent_alloc - smoothed_alloc) /
smoothing_samples;
/* Scale the estimate by a GUC to allow more aggressive tuning. */
upcoming_alloc_est = (int) (smoothed_alloc * bgwriter_lru_multiplier);
/*
* If recent_alloc remains at zero for many cycles, smoothed_alloc will
* eventually underflow to zero, and the underflows produce annoying
* kernel warnings on some platforms. Once upcoming_alloc_est has gone to
* zero, there's no point in tracking smaller and smaller values of
* smoothed_alloc, so just reset it to exactly zero to avoid this
* syndrome. It will pop back up as soon as recent_alloc increases.
*/
if (upcoming_alloc_est == 0)
smoothed_alloc = 0;
/*
* Even in cases where there's been little or no buffer allocation
* activity, we want to make a small amount of progress through the buffer
* cache so that as many reusable buffers as possible are clean after an
* idle period.
*
* (scan_whole_pool_milliseconds / BgWriterDelay) computes how many times
* the BGW will be called during the scan_whole_pool time; slice the
* buffer pool into that many sections.
*/
min_scan_buffers = (int) (NBuffers / (scan_whole_pool_milliseconds / BgWriterDelay));
if (upcoming_alloc_est < (min_scan_buffers + reusable_buffers_est))
{
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter: alloc_est=%d too small, using min=%d + reusable_est=%d",
upcoming_alloc_est, min_scan_buffers, reusable_buffers_est);
#endif
upcoming_alloc_est = min_scan_buffers + reusable_buffers_est;
}
/*
* Now write out dirty reusable buffers, working forward from the
* next_to_clean point, until we have lapped the strategy scan, or cleaned
* enough buffers to match our estimate of the next cycle's allocation
* requirements, or hit the bgwriter_lru_maxpages limit.
*/
num_to_scan = bufs_to_lap;
num_written = 0;
reusable_buffers = reusable_buffers_est;
/* Execute the LRU scan */
while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est)
{
int sync_state = SyncOneBuffer(next_to_clean, true,
wb_context);
if (++next_to_clean >= NBuffers)
{
next_to_clean = 0;
next_passes++;
}
num_to_scan--;
if (sync_state & BUF_WRITTEN)
{
reusable_buffers++;
if (++num_written >= bgwriter_lru_maxpages)
{
PendingBgWriterStats.maxwritten_clean++;
break;
}
}
else if (sync_state & BUF_REUSABLE)
reusable_buffers++;
}
PendingBgWriterStats.buf_written_clean += num_written;
#ifdef BGW_DEBUG
elog(DEBUG1, "bgwriter: recent_alloc=%u smoothed=%.2f delta=%ld ahead=%d density=%.2f reusable_est=%d upcoming_est=%d scanned=%d wrote=%d reusable=%d",
recent_alloc, smoothed_alloc, strategy_delta, bufs_ahead,
smoothed_density, reusable_buffers_est, upcoming_alloc_est,
bufs_to_lap - num_to_scan,
num_written,
reusable_buffers - reusable_buffers_est);
#endif
/*
* Consider the above scan as being like a new allocation scan.
* Characterize its density and update the smoothed one based on it. This
* effectively halves the moving average period in cases where both the
* strategy and the background writer are doing some useful scanning,
* which is helpful because a long memory isn't as desirable on the
* density estimates.
*/
new_strategy_delta = bufs_to_lap - num_to_scan;
new_recent_alloc = reusable_buffers - reusable_buffers_est;
if (new_strategy_delta > 0 && new_recent_alloc > 0)
{
scans_per_alloc = (float) new_strategy_delta / (float) new_recent_alloc;
smoothed_density += (scans_per_alloc - smoothed_density) /
smoothing_samples;
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter: cleaner density alloc=%u scan=%ld density=%.2f new smoothed=%.2f",
new_recent_alloc, new_strategy_delta,
scans_per_alloc, smoothed_density);
#endif
}
/* Return true if OK to hibernate */
return (bufs_to_lap == 0 && recent_alloc == 0);
}
/*
* SyncOneBuffer -- process a single buffer during syncing.
*
* If skip_recently_used is true, we don't write currently-pinned buffers, nor
* buffers marked recently used, as these are not replacement candidates.
*
* Returns a bitmask containing the following flag bits:
* BUF_WRITTEN: we wrote the buffer.
* BUF_REUSABLE: buffer is available for replacement, ie, it has
* pin count 0 and usage count 0.
*
* (BUF_WRITTEN could be set in error if FlushBuffer finds the buffer clean
* after locking it, but we don't care all that much.)
*/
static int
SyncOneBuffer(int buf_id, bool skip_recently_used, WritebackContext *wb_context)
{
BufferDesc *bufHdr = GetBufferDescriptor(buf_id);
int result = 0;
uint32 buf_state;
BufferTag tag;
/* Make sure we can handle the pin */
ReservePrivateRefCountEntry();
ResourceOwnerEnlarge(CurrentResourceOwner);
/*
* Check whether buffer needs writing.
*
* We can make this check without taking the buffer content lock so long
* as we mark pages dirty in access methods *before* logging changes with
* XLogInsert(): if someone marks the buffer dirty just after our check we
* don't worry because our checkpoint.redo points before log record for
* upcoming changes and so we are not required to write such dirty buffer.
*/
buf_state = LockBufHdr(bufHdr);
if (BUF_STATE_GET_REFCOUNT(buf_state) == 0 &&
BUF_STATE_GET_USAGECOUNT(buf_state) == 0)
{
result |= BUF_REUSABLE;
}
else if (skip_recently_used)
{
/* Caller told us not to write recently-used buffers */
UnlockBufHdr(bufHdr, buf_state);
return result;
}
if (!(buf_state & BM_VALID) || !(buf_state & BM_DIRTY))
{
/* It's clean, so nothing to do */
UnlockBufHdr(bufHdr, buf_state);
return result;
}
/*
* Pin it, share-lock it, write it. (FlushBuffer will do nothing if the
* buffer is clean by the time we've locked it.)
*/
PinBuffer_Locked(bufHdr);
LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_SHARED);
FlushBuffer(bufHdr, NULL, IOOBJECT_RELATION, IOCONTEXT_NORMAL);
LWLockRelease(BufferDescriptorGetContentLock(bufHdr));
tag = bufHdr->tag;
UnpinBuffer(bufHdr);
/*
* SyncOneBuffer() is only called by checkpointer and bgwriter, so
* IOContext will always be IOCONTEXT_NORMAL.
*/
ScheduleBufferTagForWriteback(wb_context, IOCONTEXT_NORMAL, &tag);
return result | BUF_WRITTEN;
}
/*
* AtEOXact_Buffers - clean up at end of transaction.
*
* As of PostgreSQL 8.0, buffer pins should get released by the
* ResourceOwner mechanism. This routine is just a debugging
* cross-check that no pins remain.
*/
void
AtEOXact_Buffers(bool isCommit)
{
CheckForBufferLeaks();
AtEOXact_LocalBuffers(isCommit);
Assert(PrivateRefCountOverflowed == 0);
}
/*
* Initialize access to shared buffer pool
*
* This is called during backend startup (whether standalone or under the
* postmaster). It sets up for this backend's access to the already-existing
* buffer pool.
*/
void
InitBufferManagerAccess(void)
{
HASHCTL hash_ctl;
memset(&PrivateRefCountArray, 0, sizeof(PrivateRefCountArray));
hash_ctl.keysize = sizeof(int32);
hash_ctl.entrysize = sizeof(PrivateRefCountEntry);
PrivateRefCountHash = hash_create("PrivateRefCount", 100, &hash_ctl,
HASH_ELEM | HASH_BLOBS);
/*
* AtProcExit_Buffers needs LWLock access, and thereby has to be called at
* the corresponding phase of backend shutdown.
*/
Assert(MyProc != NULL);
on_shmem_exit(AtProcExit_Buffers, 0);
}
/*
* During backend exit, ensure that we released all shared-buffer locks and
* assert that we have no remaining pins.
*/
static void
AtProcExit_Buffers(int code, Datum arg)
{
UnlockBuffers();
CheckForBufferLeaks();
/* localbuf.c needs a chance too */
AtProcExit_LocalBuffers();
}
/*
* CheckForBufferLeaks - ensure this backend holds no buffer pins
*
* As of PostgreSQL 8.0, buffer pins should get released by the
* ResourceOwner mechanism. This routine is just a debugging
* cross-check that no pins remain.
*/
static void
CheckForBufferLeaks(void)
{
#ifdef USE_ASSERT_CHECKING
int RefCountErrors = 0;
PrivateRefCountEntry *res;
int i;
char *s;
/* check the array */
for (i = 0; i < REFCOUNT_ARRAY_ENTRIES; i++)
{
res = &PrivateRefCountArray[i];
if (res->buffer != InvalidBuffer)
{
s = DebugPrintBufferRefcount(res->buffer);
elog(WARNING, "buffer refcount leak: %s", s);
pfree(s);
RefCountErrors++;
}
}
/* if necessary search the hash */
if (PrivateRefCountOverflowed)
{
HASH_SEQ_STATUS hstat;
hash_seq_init(&hstat, PrivateRefCountHash);
while ((res = (PrivateRefCountEntry *) hash_seq_search(&hstat)) != NULL)
{
s = DebugPrintBufferRefcount(res->buffer);
elog(WARNING, "buffer refcount leak: %s", s);
pfree(s);
RefCountErrors++;
}
}
Assert(RefCountErrors == 0);
#endif
}
/*
* Helper routine to issue warnings when a buffer is unexpectedly pinned
*/
char *
DebugPrintBufferRefcount(Buffer buffer)
{
BufferDesc *buf;
int32 loccount;
char *path;
char *result;
ProcNumber backend;
uint32 buf_state;
Assert(BufferIsValid(buffer));
if (BufferIsLocal(buffer))
{
buf = GetLocalBufferDescriptor(-buffer - 1);
loccount = LocalRefCount[-buffer - 1];
backend = MyProcNumber;
}
else
{
buf = GetBufferDescriptor(buffer - 1);
loccount = GetPrivateRefCount(buffer);
backend = INVALID_PROC_NUMBER;
}
/* theoretically we should lock the bufhdr here */
path = relpathbackend(BufTagGetRelFileLocator(&buf->tag), backend,
BufTagGetForkNum(&buf->tag));
buf_state = pg_atomic_read_u32(&buf->state);
result = psprintf("[%03d] (rel=%s, blockNum=%u, flags=0x%x, refcount=%u %d)",
buffer, path,
buf->tag.blockNum, buf_state & BUF_FLAG_MASK,
BUF_STATE_GET_REFCOUNT(buf_state), loccount);
pfree(path);
return result;
}
/*
* CheckPointBuffers
*
* Flush all dirty blocks in buffer pool to disk at checkpoint time.
*
* Note: temporary relations do not participate in checkpoints, so they don't
* need to be flushed.
*/
void
CheckPointBuffers(int flags)
{
BufferSync(flags);
}
/*
* BufferGetBlockNumber
* Returns the block number associated with a buffer.
*
* Note:
* Assumes that the buffer is valid and pinned, else the
* value may be obsolete immediately...
*/
BlockNumber
BufferGetBlockNumber(Buffer buffer)
{
BufferDesc *bufHdr;
Assert(BufferIsPinned(buffer));
if (BufferIsLocal(buffer))
bufHdr = GetLocalBufferDescriptor(-buffer - 1);
else
bufHdr = GetBufferDescriptor(buffer - 1);
/* pinned, so OK to read tag without spinlock */
return bufHdr->tag.blockNum;
}
/*
* BufferGetTag
* Returns the relfilelocator, fork number and block number associated with
* a buffer.
*/
void
BufferGetTag(Buffer buffer, RelFileLocator *rlocator, ForkNumber *forknum,
BlockNumber *blknum)
{
BufferDesc *bufHdr;
/* Do the same checks as BufferGetBlockNumber. */
Assert(BufferIsPinned(buffer));
if (BufferIsLocal(buffer))
bufHdr = GetLocalBufferDescriptor(-buffer - 1);
else
bufHdr = GetBufferDescriptor(buffer - 1);
/* pinned, so OK to read tag without spinlock */
*rlocator = BufTagGetRelFileLocator(&bufHdr->tag);
*forknum = BufTagGetForkNum(&bufHdr->tag);
*blknum = bufHdr->tag.blockNum;
}
/*
* FlushBuffer
* Physically write out a shared buffer.
*
* NOTE: this actually just passes the buffer contents to the kernel; the
* real write to disk won't happen until the kernel feels like it. This
* is okay from our point of view since we can redo the changes from WAL.
* However, we will need to force the changes to disk via fsync before
* we can checkpoint WAL.
*
* The caller must hold a pin on the buffer and have share-locked the
* buffer contents. (Note: a share-lock does not prevent updates of
* hint bits in the buffer, so the page could change while the write
* is in progress, but we assume that that will not invalidate the data
* written.)
*
* If the caller has an smgr reference for the buffer's relation, pass it
* as the second parameter. If not, pass NULL.
*/
static void
FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object,
IOContext io_context)
{
XLogRecPtr recptr;
ErrorContextCallback errcallback;
instr_time io_start;
Block bufBlock;
char *bufToWrite;
uint32 buf_state;
/*
* Try to start an I/O operation. If StartBufferIO returns false, then
* someone else flushed the buffer before we could, so we need not do
* anything.
*/
if (!StartBufferIO(buf, false, false))
return;
/* Setup error traceback support for ereport() */
errcallback.callback = shared_buffer_write_error_callback;
errcallback.arg = buf;
errcallback.previous = error_context_stack;
error_context_stack = &errcallback;
/* Find smgr relation for buffer */
if (reln == NULL)
reln = smgropen(BufTagGetRelFileLocator(&buf->tag), INVALID_PROC_NUMBER);
TRACE_POSTGRESQL_BUFFER_FLUSH_START(BufTagGetForkNum(&buf->tag),
buf->tag.blockNum,
reln->smgr_rlocator.locator.spcOid,
reln->smgr_rlocator.locator.dbOid,
reln->smgr_rlocator.locator.relNumber);
buf_state = LockBufHdr(buf);
/*
* Run PageGetLSN while holding header lock, since we don't have the
* buffer locked exclusively in all cases.
*/
recptr = BufferGetLSN(buf);
/* To check if block content changes while flushing. - vadim 01/17/97 */
buf_state &= ~BM_JUST_DIRTIED;
UnlockBufHdr(buf, buf_state);
/*
* Force XLOG flush up to buffer's LSN. This implements the basic WAL
* rule that log updates must hit disk before any of the data-file changes
* they describe do.
*
* However, this rule does not apply to unlogged relations, which will be
* lost after a crash anyway. Most unlogged relation pages do not bear
* LSNs since we never emit WAL records for them, and therefore flushing
* up through the buffer LSN would be useless, but harmless. However,
* GiST indexes use LSNs internally to track page-splits, and therefore
* unlogged GiST pages bear "fake" LSNs generated by
* GetFakeLSNForUnloggedRel. It is unlikely but possible that the fake
* LSN counter could advance past the WAL insertion point; and if it did
* happen, attempting to flush WAL through that location would fail, with
* disastrous system-wide consequences. To make sure that can't happen,
* skip the flush if the buffer isn't permanent.
*/
if (buf_state & BM_PERMANENT)
XLogFlush(recptr);
/*
* Now it's safe to write buffer to disk. Note that no one else should
* have been able to write it while we were busy with log flushing because
* only one process at a time can set the BM_IO_IN_PROGRESS bit.
*/
bufBlock = BufHdrGetBlock(buf);
/*
* Update page checksum if desired. Since we have only shared lock on the
* buffer, other processes might be updating hint bits in it, so we must
* copy the page to private storage if we do checksumming.
*/
bufToWrite = PageSetChecksumCopy((Page) bufBlock, buf->tag.blockNum);
io_start = pgstat_prepare_io_time(track_io_timing);
/*
* bufToWrite is either the shared buffer or a copy, as appropriate.
*/
smgrwrite(reln,
BufTagGetForkNum(&buf->tag),
buf->tag.blockNum,
bufToWrite,
false);
/*
* When a strategy is in use, only flushes of dirty buffers already in the
* strategy ring are counted as strategy writes (IOCONTEXT
* [BULKREAD|BULKWRITE|VACUUM] IOOP_WRITE) for the purpose of IO
* statistics tracking.
*
* If a shared buffer initially added to the ring must be flushed before
* being used, this is counted as an IOCONTEXT_NORMAL IOOP_WRITE.
*
* If a shared buffer which was added to the ring later because the
* current strategy buffer is pinned or in use or because all strategy
* buffers were dirty and rejected (for BAS_BULKREAD operations only)
* requires flushing, this is counted as an IOCONTEXT_NORMAL IOOP_WRITE
* (from_ring will be false).
*
* When a strategy is not in use, the write can only be a "regular" write
* of a dirty shared buffer (IOCONTEXT_NORMAL IOOP_WRITE).
*/
pgstat_count_io_op_time(IOOBJECT_RELATION, io_context,
IOOP_WRITE, io_start, 1);
pgBufferUsage.shared_blks_written++;
/*
* Mark the buffer as clean (unless BM_JUST_DIRTIED has become set) and
* end the BM_IO_IN_PROGRESS state.
*/
TerminateBufferIO(buf, true, 0, true);
TRACE_POSTGRESQL_BUFFER_FLUSH_DONE(BufTagGetForkNum(&buf->tag),
buf->tag.blockNum,
reln->smgr_rlocator.locator.spcOid,
reln->smgr_rlocator.locator.dbOid,
reln->smgr_rlocator.locator.relNumber);
/* Pop the error context stack */
error_context_stack = errcallback.previous;
}
/*
* RelationGetNumberOfBlocksInFork
* Determines the current number of pages in the specified relation fork.
*
* Note that the accuracy of the result will depend on the details of the
* relation's storage. For builtin AMs it'll be accurate, but for external AMs
* it might not be.
*/
BlockNumber
RelationGetNumberOfBlocksInFork(Relation relation, ForkNumber forkNum)
{
if (RELKIND_HAS_TABLE_AM(relation->rd_rel->relkind))
{
/*
* Not every table AM uses BLCKSZ wide fixed size blocks. Therefore
* tableam returns the size in bytes - but for the purpose of this
* routine, we want the number of blocks. Therefore divide, rounding
* up.
*/
uint64 szbytes;
szbytes = table_relation_size(relation, forkNum);
return (szbytes + (BLCKSZ - 1)) / BLCKSZ;
}
else if (RELKIND_HAS_STORAGE(relation->rd_rel->relkind))
{
return smgrnblocks(RelationGetSmgr(relation), forkNum);
}
else
Assert(false);
return 0; /* keep compiler quiet */
}
/*
* BufferIsPermanent
* Determines whether a buffer will potentially still be around after
* a crash. Caller must hold a buffer pin.
*/
bool
BufferIsPermanent(Buffer buffer)
{
BufferDesc *bufHdr;
/* Local buffers are used only for temp relations. */
if (BufferIsLocal(buffer))
return false;
/* Make sure we've got a real buffer, and that we hold a pin on it. */
Assert(BufferIsValid(buffer));
Assert(BufferIsPinned(buffer));
/*
* BM_PERMANENT can't be changed while we hold a pin on the buffer, so we
* need not bother with the buffer header spinlock. Even if someone else
* changes the buffer header state while we're doing this, the state is
* changed atomically, so we'll read the old value or the new value, but
* not random garbage.
*/
bufHdr = GetBufferDescriptor(buffer - 1);
return (pg_atomic_read_u32(&bufHdr->state) & BM_PERMANENT) != 0;
}
/*
* BufferGetLSNAtomic
* Retrieves the LSN of the buffer atomically using a buffer header lock.
* This is necessary for some callers who may not have an exclusive lock
* on the buffer.
*/
XLogRecPtr
BufferGetLSNAtomic(Buffer buffer)
{
BufferDesc *bufHdr = GetBufferDescriptor(buffer - 1);
char *page = BufferGetPage(buffer);
XLogRecPtr lsn;
uint32 buf_state;
/*
* If we don't need locking for correctness, fastpath out.
*/
if (!XLogHintBitIsNeeded() || BufferIsLocal(buffer))
return PageGetLSN(page);
/* Make sure we've got a real buffer, and that we hold a pin on it. */
Assert(BufferIsValid(buffer));
Assert(BufferIsPinned(buffer));
buf_state = LockBufHdr(bufHdr);
lsn = PageGetLSN(page);
UnlockBufHdr(bufHdr, buf_state);
return lsn;
}
/* ---------------------------------------------------------------------
* DropRelationBuffers
*
* This function removes from the buffer pool all the pages of the
* specified relation forks that have block numbers >= firstDelBlock.
* (In particular, with firstDelBlock = 0, all pages are removed.)
* Dirty pages are simply dropped, without bothering to write them
* out first. Therefore, this is NOT rollback-able, and so should be
* used only with extreme caution!
*
* Currently, this is called only from smgr.c when the underlying file
* is about to be deleted or truncated (firstDelBlock is needed for
* the truncation case). The data in the affected pages would therefore
* be deleted momentarily anyway, and there is no point in writing it.
* It is the responsibility of higher-level code to ensure that the
* deletion or truncation does not lose any data that could be needed
* later. It is also the responsibility of higher-level code to ensure
* that no other process could be trying to load more pages of the
* relation into buffers.
* --------------------------------------------------------------------
*/
void
DropRelationBuffers(SMgrRelation smgr_reln, ForkNumber *forkNum,
int nforks, BlockNumber *firstDelBlock)
{
int i;
int j;
RelFileLocatorBackend rlocator;
BlockNumber nForkBlock[MAX_FORKNUM];
uint64 nBlocksToInvalidate = 0;
rlocator = smgr_reln->smgr_rlocator;
/* If it's a local relation, it's localbuf.c's problem. */
if (RelFileLocatorBackendIsTemp(rlocator))
{
if (rlocator.backend == MyProcNumber)
{
for (j = 0; j < nforks; j++)
DropRelationLocalBuffers(rlocator.locator, forkNum[j],
firstDelBlock[j]);
}
return;
}
/*
* To remove all the pages of the specified relation forks from the buffer
* pool, we need to scan the entire buffer pool but we can optimize it by
* finding the buffers from BufMapping table provided we know the exact
* size of each fork of the relation. The exact size is required to ensure
* that we don't leave any buffer for the relation being dropped as
* otherwise the background writer or checkpointer can lead to a PANIC
* error while flushing buffers corresponding to files that don't exist.
*
* To know the exact size, we rely on the size cached for each fork by us
* during recovery which limits the optimization to recovery and on
* standbys but we can easily extend it once we have shared cache for
* relation size.
*
* In recovery, we cache the value returned by the first lseek(SEEK_END)
* and the future writes keeps the cached value up-to-date. See
* smgrextend. It is possible that the value of the first lseek is smaller
* than the actual number of existing blocks in the file due to buggy
* Linux kernels that might not have accounted for the recent write. But
* that should be fine because there must not be any buffers after that
* file size.
*/
for (i = 0; i < nforks; i++)
{
/* Get the number of blocks for a relation's fork */
nForkBlock[i] = smgrnblocks_cached(smgr_reln, forkNum[i]);
if (nForkBlock[i] == InvalidBlockNumber)
{
nBlocksToInvalidate = InvalidBlockNumber;
break;
}
/* calculate the number of blocks to be invalidated */
nBlocksToInvalidate += (nForkBlock[i] - firstDelBlock[i]);
}
/*
* We apply the optimization iff the total number of blocks to invalidate
* is below the BUF_DROP_FULL_SCAN_THRESHOLD.
*/
if (BlockNumberIsValid(nBlocksToInvalidate) &&
nBlocksToInvalidate < BUF_DROP_FULL_SCAN_THRESHOLD)
{
for (j = 0; j < nforks; j++)
FindAndDropRelationBuffers(rlocator.locator, forkNum[j],
nForkBlock[j], firstDelBlock[j]);
return;
}
for (i = 0; i < NBuffers; i++)
{
BufferDesc *bufHdr = GetBufferDescriptor(i);
uint32 buf_state;
/*
* We can make this a tad faster by prechecking the buffer tag before
* we attempt to lock the buffer; this saves a lot of lock
* acquisitions in typical cases. It should be safe because the
* caller must have AccessExclusiveLock on the relation, or some other
* reason to be certain that no one is loading new pages of the rel
* into the buffer pool. (Otherwise we might well miss such pages
* entirely.) Therefore, while the tag might be changing while we
* look at it, it can't be changing *to* a value we care about, only
* *away* from such a value. So false negatives are impossible, and
* false positives are safe because we'll recheck after getting the
* buffer lock.
*
* We could check forkNum and blockNum as well as the rlocator, but
* the incremental win from doing so seems small.
*/
if (!BufTagMatchesRelFileLocator(&bufHdr->tag, &rlocator.locator))
continue;
buf_state = LockBufHdr(bufHdr);
for (j = 0; j < nforks; j++)
{
if (BufTagMatchesRelFileLocator(&bufHdr->tag, &rlocator.locator) &&
BufTagGetForkNum(&bufHdr->tag) == forkNum[j] &&
bufHdr->tag.blockNum >= firstDelBlock[j])
{
InvalidateBuffer(bufHdr); /* releases spinlock */
break;
}
}
if (j >= nforks)
UnlockBufHdr(bufHdr, buf_state);
}
}
/* ---------------------------------------------------------------------
* DropRelationsAllBuffers
*
* This function removes from the buffer pool all the pages of all
* forks of the specified relations. It's equivalent to calling
* DropRelationBuffers once per fork per relation with firstDelBlock = 0.
* --------------------------------------------------------------------
*/
void
DropRelationsAllBuffers(SMgrRelation *smgr_reln, int nlocators)
{
int i;
int n = 0;
SMgrRelation *rels;
BlockNumber (*block)[MAX_FORKNUM + 1];
uint64 nBlocksToInvalidate = 0;
RelFileLocator *locators;
bool cached = true;
bool use_bsearch;
if (nlocators == 0)
return;
rels = palloc(sizeof(SMgrRelation) * nlocators); /* non-local relations */
/* If it's a local relation, it's localbuf.c's problem. */
for (i = 0; i < nlocators; i++)
{
if (RelFileLocatorBackendIsTemp(smgr_reln[i]->smgr_rlocator))
{
if (smgr_reln[i]->smgr_rlocator.backend == MyProcNumber)
DropRelationAllLocalBuffers(smgr_reln[i]->smgr_rlocator.locator);
}
else
rels[n++] = smgr_reln[i];
}
/*
* If there are no non-local relations, then we're done. Release the
* memory and return.
*/
if (n == 0)
{
pfree(rels);
return;
}
/*
* This is used to remember the number of blocks for all the relations
* forks.
*/
block = (BlockNumber (*)[MAX_FORKNUM + 1])
palloc(sizeof(BlockNumber) * n * (MAX_FORKNUM + 1));
/*
* We can avoid scanning the entire buffer pool if we know the exact size
* of each of the given relation forks. See DropRelationBuffers.
*/
for (i = 0; i < n && cached; i++)
{
for (int j = 0; j <= MAX_FORKNUM; j++)
{
/* Get the number of blocks for a relation's fork. */
block[i][j] = smgrnblocks_cached(rels[i], j);
/* We need to only consider the relation forks that exists. */
if (block[i][j] == InvalidBlockNumber)
{
if (!smgrexists(rels[i], j))
continue;
cached = false;
break;
}
/* calculate the total number of blocks to be invalidated */
nBlocksToInvalidate += block[i][j];
}
}
/*
* We apply the optimization iff the total number of blocks to invalidate
* is below the BUF_DROP_FULL_SCAN_THRESHOLD.
*/
if (cached && nBlocksToInvalidate < BUF_DROP_FULL_SCAN_THRESHOLD)
{
for (i = 0; i < n; i++)
{
for (int j = 0; j <= MAX_FORKNUM; j++)
{
/* ignore relation forks that doesn't exist */
if (!BlockNumberIsValid(block[i][j]))
continue;
/* drop all the buffers for a particular relation fork */
FindAndDropRelationBuffers(rels[i]->smgr_rlocator.locator,
j, block[i][j], 0);
}
}
pfree(block);
pfree(rels);
return;
}
pfree(block);
locators = palloc(sizeof(RelFileLocator) * n); /* non-local relations */
for (i = 0; i < n; i++)
locators[i] = rels[i]->smgr_rlocator.locator;
/*
* For low number of relations to drop just use a simple walk through, to
* save the bsearch overhead. The threshold to use is rather a guess than
* an exactly determined value, as it depends on many factors (CPU and RAM
* speeds, amount of shared buffers etc.).
*/
use_bsearch = n > RELS_BSEARCH_THRESHOLD;
/* sort the list of rlocators if necessary */
if (use_bsearch)
qsort(locators, n, sizeof(RelFileLocator), rlocator_comparator);
for (i = 0; i < NBuffers; i++)
{
RelFileLocator *rlocator = NULL;
BufferDesc *bufHdr = GetBufferDescriptor(i);
uint32 buf_state;
/*
* As in DropRelationBuffers, an unlocked precheck should be safe and
* saves some cycles.
*/
if (!use_bsearch)
{
int j;
for (j = 0; j < n; j++)
{
if (BufTagMatchesRelFileLocator(&bufHdr->tag, &locators[j]))
{
rlocator = &locators[j];
break;
}
}
}
else
{
RelFileLocator locator;
locator = BufTagGetRelFileLocator(&bufHdr->tag);
rlocator = bsearch(&locator,
locators, n, sizeof(RelFileLocator),
rlocator_comparator);
}
/* buffer doesn't belong to any of the given relfilelocators; skip it */
if (rlocator == NULL)
continue;
buf_state = LockBufHdr(bufHdr);
if (BufTagMatchesRelFileLocator(&bufHdr->tag, rlocator))
InvalidateBuffer(bufHdr); /* releases spinlock */
else
UnlockBufHdr(bufHdr, buf_state);
}
pfree(locators);
pfree(rels);
}
/* ---------------------------------------------------------------------
* FindAndDropRelationBuffers
*
* This function performs look up in BufMapping table and removes from the
* buffer pool all the pages of the specified relation fork that has block
* number >= firstDelBlock. (In particular, with firstDelBlock = 0, all
* pages are removed.)
* --------------------------------------------------------------------
*/
static void
FindAndDropRelationBuffers(RelFileLocator rlocator, ForkNumber forkNum,
BlockNumber nForkBlock,
BlockNumber firstDelBlock)
{
BlockNumber curBlock;
for (curBlock = firstDelBlock; curBlock < nForkBlock; curBlock++)
{
uint32 bufHash; /* hash value for tag */
BufferTag bufTag; /* identity of requested block */
LWLock *bufPartitionLock; /* buffer partition lock for it */
int buf_id;
BufferDesc *bufHdr;
uint32 buf_state;
/* create a tag so we can lookup the buffer */
InitBufferTag(&bufTag, &rlocator, forkNum, curBlock);
/* determine its hash code and partition lock ID */
bufHash = BufTableHashCode(&bufTag);
bufPartitionLock = BufMappingPartitionLock(bufHash);
/* Check that it is in the buffer pool. If not, do nothing. */
LWLockAcquire(bufPartitionLock, LW_SHARED);
buf_id = BufTableLookup(&bufTag, bufHash);
LWLockRelease(bufPartitionLock);
if (buf_id < 0)
continue;
bufHdr = GetBufferDescriptor(buf_id);
/*
* We need to lock the buffer header and recheck if the buffer is
* still associated with the same block because the buffer could be
* evicted by some other backend loading blocks for a different
* relation after we release lock on the BufMapping table.
*/
buf_state = LockBufHdr(bufHdr);
if (BufTagMatchesRelFileLocator(&bufHdr->tag, &rlocator) &&
BufTagGetForkNum(&bufHdr->tag) == forkNum &&
bufHdr->tag.blockNum >= firstDelBlock)
InvalidateBuffer(bufHdr); /* releases spinlock */
else
UnlockBufHdr(bufHdr, buf_state);
}
}
/* ---------------------------------------------------------------------
* DropDatabaseBuffers
*
* This function removes all the buffers in the buffer cache for a
* particular database. Dirty pages are simply dropped, without
* bothering to write them out first. This is used when we destroy a
* database, to avoid trying to flush data to disk when the directory
* tree no longer exists. Implementation is pretty similar to
* DropRelationBuffers() which is for destroying just one relation.
* --------------------------------------------------------------------
*/
void
DropDatabaseBuffers(Oid dbid)
{
int i;
/*
* We needn't consider local buffers, since by assumption the target
* database isn't our own.
*/
for (i = 0; i < NBuffers; i++)
{
BufferDesc *bufHdr = GetBufferDescriptor(i);
uint32 buf_state;
/*
* As in DropRelationBuffers, an unlocked precheck should be safe and
* saves some cycles.
*/
if (bufHdr->tag.dbOid != dbid)
continue;
buf_state = LockBufHdr(bufHdr);
if (bufHdr->tag.dbOid == dbid)
InvalidateBuffer(bufHdr); /* releases spinlock */
else
UnlockBufHdr(bufHdr, buf_state);
}
}
/* -----------------------------------------------------------------
* PrintBufferDescs
*
* this function prints all the buffer descriptors, for debugging
* use only.
* -----------------------------------------------------------------
*/
#ifdef NOT_USED
void
PrintBufferDescs(void)
{
int i;
for (i = 0; i < NBuffers; ++i)
{
BufferDesc *buf = GetBufferDescriptor(i);
Buffer b = BufferDescriptorGetBuffer(buf);
/* theoretically we should lock the bufhdr here */
elog(LOG,
"[%02d] (freeNext=%d, rel=%s, "
"blockNum=%u, flags=0x%x, refcount=%u %d)",
i, buf->freeNext,
relpathbackend(BufTagGetRelFileLocator(&buf->tag),
INVALID_PROC_NUMBER, BufTagGetForkNum(&buf->tag)),
buf->tag.blockNum, buf->flags,
buf->refcount, GetPrivateRefCount(b));
}
}
#endif
#ifdef NOT_USED
void
PrintPinnedBufs(void)
{
int i;
for (i = 0; i < NBuffers; ++i)
{
BufferDesc *buf = GetBufferDescriptor(i);
Buffer b = BufferDescriptorGetBuffer(buf);
if (GetPrivateRefCount(b) > 0)
{
/* theoretically we should lock the bufhdr here */
elog(LOG,
"[%02d] (freeNext=%d, rel=%s, "
"blockNum=%u, flags=0x%x, refcount=%u %d)",
i, buf->freeNext,
relpathperm(BufTagGetRelFileLocator(&buf->tag),
BufTagGetForkNum(&buf->tag)),
buf->tag.blockNum, buf->flags,
buf->refcount, GetPrivateRefCount(b));
}
}
}
#endif
/* ---------------------------------------------------------------------
* FlushRelationBuffers
*
* This function writes all dirty pages of a relation out to disk
* (or more accurately, out to kernel disk buffers), ensuring that the
* kernel has an up-to-date view of the relation.
*
* Generally, the caller should be holding AccessExclusiveLock on the
* target relation to ensure that no other backend is busy dirtying
* more blocks of the relation; the effects can't be expected to last
* after the lock is released.
*
* XXX currently it sequentially searches the buffer pool, should be
* changed to more clever ways of searching. This routine is not
* used in any performance-critical code paths, so it's not worth
* adding additional overhead to normal paths to make it go faster.
* --------------------------------------------------------------------
*/
void
FlushRelationBuffers(Relation rel)
{
int i;
BufferDesc *bufHdr;
SMgrRelation srel = RelationGetSmgr(rel);
if (RelationUsesLocalBuffers(rel))
{
for (i = 0; i < NLocBuffer; i++)
{
uint32 buf_state;
instr_time io_start;
bufHdr = GetLocalBufferDescriptor(i);
if (BufTagMatchesRelFileLocator(&bufHdr->tag, &rel->rd_locator) &&
((buf_state = pg_atomic_read_u32(&bufHdr->state)) &
(BM_VALID | BM_DIRTY)) == (BM_VALID | BM_DIRTY))
{
ErrorContextCallback errcallback;
Page localpage;
localpage = (char *) LocalBufHdrGetBlock(bufHdr);
/* Setup error traceback support for ereport() */
errcallback.callback = local_buffer_write_error_callback;
errcallback.arg = bufHdr;
errcallback.previous = error_context_stack;
error_context_stack = &errcallback;
PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
io_start = pgstat_prepare_io_time(track_io_timing);
smgrwrite(srel,
BufTagGetForkNum(&bufHdr->tag),
bufHdr->tag.blockNum,
localpage,
false);
pgstat_count_io_op_time(IOOBJECT_TEMP_RELATION,
IOCONTEXT_NORMAL, IOOP_WRITE,
io_start, 1);
buf_state &= ~(BM_DIRTY | BM_JUST_DIRTIED);
pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
pgBufferUsage.local_blks_written++;
/* Pop the error context stack */
error_context_stack = errcallback.previous;
}
}
return;
}
for (i = 0; i < NBuffers; i++)
{
uint32 buf_state;
bufHdr = GetBufferDescriptor(i);
/*
* As in DropRelationBuffers, an unlocked precheck should be safe and
* saves some cycles.
*/
if (!BufTagMatchesRelFileLocator(&bufHdr->tag, &rel->rd_locator))
continue;
/* Make sure we can handle the pin */
ReservePrivateRefCountEntry();
ResourceOwnerEnlarge(CurrentResourceOwner);
buf_state = LockBufHdr(bufHdr);
if (BufTagMatchesRelFileLocator(&bufHdr->tag, &rel->rd_locator) &&
(buf_state & (BM_VALID | BM_DIRTY)) == (BM_VALID | BM_DIRTY))
{
PinBuffer_Locked(bufHdr);
LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_SHARED);
FlushBuffer(bufHdr, srel, IOOBJECT_RELATION, IOCONTEXT_NORMAL);
LWLockRelease(BufferDescriptorGetContentLock(bufHdr));
UnpinBuffer(bufHdr);
}
else
UnlockBufHdr(bufHdr, buf_state);
}
}
/* ---------------------------------------------------------------------
* FlushRelationsAllBuffers
*
* This function flushes out of the buffer pool all the pages of all
* forks of the specified smgr relations. It's equivalent to calling
* FlushRelationBuffers once per relation. The relations are assumed not
* to use local buffers.
* --------------------------------------------------------------------
*/
void
FlushRelationsAllBuffers(SMgrRelation *smgrs, int nrels)
{
int i;
SMgrSortArray *srels;
bool use_bsearch;
if (nrels == 0)
return;
/* fill-in array for qsort */
srels = palloc(sizeof(SMgrSortArray) * nrels);
for (i = 0; i < nrels; i++)
{
Assert(!RelFileLocatorBackendIsTemp(smgrs[i]->smgr_rlocator));
srels[i].rlocator = smgrs[i]->smgr_rlocator.locator;
srels[i].srel = smgrs[i];
}
/*
* Save the bsearch overhead for low number of relations to sync. See
* DropRelationsAllBuffers for details.
*/
use_bsearch = nrels > RELS_BSEARCH_THRESHOLD;
/* sort the list of SMgrRelations if necessary */
if (use_bsearch)
qsort(srels, nrels, sizeof(SMgrSortArray), rlocator_comparator);
for (i = 0; i < NBuffers; i++)
{
SMgrSortArray *srelent = NULL;
BufferDesc *bufHdr = GetBufferDescriptor(i);
uint32 buf_state;
/*
* As in DropRelationBuffers, an unlocked precheck should be safe and
* saves some cycles.
*/
if (!use_bsearch)
{
int j;
for (j = 0; j < nrels; j++)
{
if (BufTagMatchesRelFileLocator(&bufHdr->tag, &srels[j].rlocator))
{
srelent = &srels[j];
break;
}
}
}
else
{
RelFileLocator rlocator;
rlocator = BufTagGetRelFileLocator(&bufHdr->tag);
srelent = bsearch(&rlocator,
srels, nrels, sizeof(SMgrSortArray),
rlocator_comparator);
}
/* buffer doesn't belong to any of the given relfilelocators; skip it */
if (srelent == NULL)
continue;
/* Make sure we can handle the pin */
ReservePrivateRefCountEntry();
ResourceOwnerEnlarge(CurrentResourceOwner);
buf_state = LockBufHdr(bufHdr);
if (BufTagMatchesRelFileLocator(&bufHdr->tag, &srelent->rlocator) &&
(buf_state & (BM_VALID | BM_DIRTY)) == (BM_VALID | BM_DIRTY))
{
PinBuffer_Locked(bufHdr);
LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_SHARED);
FlushBuffer(bufHdr, srelent->srel, IOOBJECT_RELATION, IOCONTEXT_NORMAL);
LWLockRelease(BufferDescriptorGetContentLock(bufHdr));
UnpinBuffer(bufHdr);
}
else
UnlockBufHdr(bufHdr, buf_state);
}
pfree(srels);
}
/* ---------------------------------------------------------------------
* RelationCopyStorageUsingBuffer
*
* Copy fork's data using bufmgr. Same as RelationCopyStorage but instead
* of using smgrread and smgrextend this will copy using bufmgr APIs.
*
* Refer comments atop CreateAndCopyRelationData() for details about
* 'permanent' parameter.
* --------------------------------------------------------------------
*/
static void
RelationCopyStorageUsingBuffer(RelFileLocator srclocator,
RelFileLocator dstlocator,
ForkNumber forkNum, bool permanent)
{
Buffer srcBuf;
Buffer dstBuf;
Page srcPage;
Page dstPage;
bool use_wal;
BlockNumber nblocks;
BlockNumber blkno;
PGIOAlignedBlock buf;
BufferAccessStrategy bstrategy_src;
BufferAccessStrategy bstrategy_dst;
BlockRangeReadStreamPrivate p;
ReadStream *src_stream;
SMgrRelation src_smgr;
/*
* In general, we want to write WAL whenever wal_level > 'minimal', but we
* can skip it when copying any fork of an unlogged relation other than
* the init fork.
*/
use_wal = XLogIsNeeded() && (permanent || forkNum == INIT_FORKNUM);
/* Get number of blocks in the source relation. */
nblocks = smgrnblocks(smgropen(srclocator, INVALID_PROC_NUMBER),
forkNum);
/* Nothing to copy; just return. */
if (nblocks == 0)
return;
/*
* Bulk extend the destination relation of the same size as the source
* relation before starting to copy block by block.
*/
memset(buf.data, 0, BLCKSZ);
smgrextend(smgropen(dstlocator, INVALID_PROC_NUMBER), forkNum, nblocks - 1,
buf.data, true);
/* This is a bulk operation, so use buffer access strategies. */
bstrategy_src = GetAccessStrategy(BAS_BULKREAD);
bstrategy_dst = GetAccessStrategy(BAS_BULKWRITE);
/* Initialize streaming read */
p.current_blocknum = 0;
p.last_exclusive = nblocks;
src_smgr = smgropen(srclocator, INVALID_PROC_NUMBER);
src_stream = read_stream_begin_smgr_relation(READ_STREAM_FULL,
bstrategy_src,
src_smgr,
permanent ? RELPERSISTENCE_PERMANENT : RELPERSISTENCE_UNLOGGED,
forkNum,
block_range_read_stream_cb,
&p,
0);
/* Iterate over each block of the source relation file. */
for (blkno = 0; blkno < nblocks; blkno++)
{
CHECK_FOR_INTERRUPTS();
/* Read block from source relation. */
srcBuf = read_stream_next_buffer(src_stream, NULL);
LockBuffer(srcBuf, BUFFER_LOCK_SHARE);
srcPage = BufferGetPage(srcBuf);
dstBuf = ReadBufferWithoutRelcache(dstlocator, forkNum,
BufferGetBlockNumber(srcBuf),
RBM_ZERO_AND_LOCK, bstrategy_dst,
permanent);
dstPage = BufferGetPage(dstBuf);
START_CRIT_SECTION();
/* Copy page data from the source to the destination. */
memcpy(dstPage, srcPage, BLCKSZ);
MarkBufferDirty(dstBuf);
/* WAL-log the copied page. */
if (use_wal)
log_newpage_buffer(dstBuf, true);
END_CRIT_SECTION();
UnlockReleaseBuffer(dstBuf);
UnlockReleaseBuffer(srcBuf);
}
Assert(read_stream_next_buffer(src_stream, NULL) == InvalidBuffer);
read_stream_end(src_stream);
FreeAccessStrategy(bstrategy_src);
FreeAccessStrategy(bstrategy_dst);
}
/* ---------------------------------------------------------------------
* CreateAndCopyRelationData
*
* Create destination relation storage and copy all forks from the
* source relation to the destination.
*
* Pass permanent as true for permanent relations and false for
* unlogged relations. Currently this API is not supported for
* temporary relations.
* --------------------------------------------------------------------
*/
void
CreateAndCopyRelationData(RelFileLocator src_rlocator,
RelFileLocator dst_rlocator, bool permanent)
{
char relpersistence;
SMgrRelation src_rel;
SMgrRelation dst_rel;
/* Set the relpersistence. */
relpersistence = permanent ?
RELPERSISTENCE_PERMANENT : RELPERSISTENCE_UNLOGGED;
src_rel = smgropen(src_rlocator, INVALID_PROC_NUMBER);
dst_rel = smgropen(dst_rlocator, INVALID_PROC_NUMBER);
/*
* Create and copy all forks of the relation. During create database we
* have a separate cleanup mechanism which deletes complete database
* directory. Therefore, each individual relation doesn't need to be
* registered for cleanup.
*/
RelationCreateStorage(dst_rlocator, relpersistence, false);
/* copy main fork. */
RelationCopyStorageUsingBuffer(src_rlocator, dst_rlocator, MAIN_FORKNUM,
permanent);
/* copy those extra forks that exist */
for (ForkNumber forkNum = MAIN_FORKNUM + 1;
forkNum <= MAX_FORKNUM; forkNum++)
{
if (smgrexists(src_rel, forkNum))
{
smgrcreate(dst_rel, forkNum, false);
/*
* WAL log creation if the relation is persistent, or this is the
* init fork of an unlogged relation.
*/
if (permanent || forkNum == INIT_FORKNUM)
log_smgrcreate(&dst_rlocator, forkNum);
/* Copy a fork's data, block by block. */
RelationCopyStorageUsingBuffer(src_rlocator, dst_rlocator, forkNum,
permanent);
}
}
}
/* ---------------------------------------------------------------------
* FlushDatabaseBuffers
*
* This function writes all dirty pages of a database out to disk
* (or more accurately, out to kernel disk buffers), ensuring that the
* kernel has an up-to-date view of the database.
*
* Generally, the caller should be holding an appropriate lock to ensure
* no other backend is active in the target database; otherwise more
* pages could get dirtied.
*
* Note we don't worry about flushing any pages of temporary relations.
* It's assumed these wouldn't be interesting.
* --------------------------------------------------------------------
*/
void
FlushDatabaseBuffers(Oid dbid)
{
int i;
BufferDesc *bufHdr;
for (i = 0; i < NBuffers; i++)
{
uint32 buf_state;
bufHdr = GetBufferDescriptor(i);
/*
* As in DropRelationBuffers, an unlocked precheck should be safe and
* saves some cycles.
*/
if (bufHdr->tag.dbOid != dbid)
continue;
/* Make sure we can handle the pin */
ReservePrivateRefCountEntry();
ResourceOwnerEnlarge(CurrentResourceOwner);
buf_state = LockBufHdr(bufHdr);
if (bufHdr->tag.dbOid == dbid &&
(buf_state & (BM_VALID | BM_DIRTY)) == (BM_VALID | BM_DIRTY))
{
PinBuffer_Locked(bufHdr);
LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_SHARED);
FlushBuffer(bufHdr, NULL, IOOBJECT_RELATION, IOCONTEXT_NORMAL);
LWLockRelease(BufferDescriptorGetContentLock(bufHdr));
UnpinBuffer(bufHdr);
}
else
UnlockBufHdr(bufHdr, buf_state);
}
}
/*
* Flush a previously, shared or exclusively, locked and pinned buffer to the
* OS.
*/
void
FlushOneBuffer(Buffer buffer)
{
BufferDesc *bufHdr;
/* currently not needed, but no fundamental reason not to support */
Assert(!BufferIsLocal(buffer));
Assert(BufferIsPinned(buffer));
bufHdr = GetBufferDescriptor(buffer - 1);
Assert(LWLockHeldByMe(BufferDescriptorGetContentLock(bufHdr)));
FlushBuffer(bufHdr, NULL, IOOBJECT_RELATION, IOCONTEXT_NORMAL);
}
/*
* ReleaseBuffer -- release the pin on a buffer
*/
void
ReleaseBuffer(Buffer buffer)
{
if (!BufferIsValid(buffer))
elog(ERROR, "bad buffer ID: %d", buffer);
if (BufferIsLocal(buffer))
UnpinLocalBuffer(buffer);
else
UnpinBuffer(GetBufferDescriptor(buffer - 1));
}
/*
* UnlockReleaseBuffer -- release the content lock and pin on a buffer
*
* This is just a shorthand for a common combination.
*/
void
UnlockReleaseBuffer(Buffer buffer)
{
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
ReleaseBuffer(buffer);
}
/*
* IncrBufferRefCount
* Increment the pin count on a buffer that we have *already* pinned
* at least once.
*
* This function cannot be used on a buffer we do not have pinned,
* because it doesn't change the shared buffer state.
*/
void
IncrBufferRefCount(Buffer buffer)
{
Assert(BufferIsPinned(buffer));
ResourceOwnerEnlarge(CurrentResourceOwner);
if (BufferIsLocal(buffer))
LocalRefCount[-buffer - 1]++;
else
{
PrivateRefCountEntry *ref;
ref = GetPrivateRefCountEntry(buffer, true);
Assert(ref != NULL);
ref->refcount++;
}
ResourceOwnerRememberBuffer(CurrentResourceOwner, buffer);
}
/*
* MarkBufferDirtyHint
*
* Mark a buffer dirty for non-critical changes.
*
* This is essentially the same as MarkBufferDirty, except:
*
* 1. The caller does not write WAL; so if checksums are enabled, we may need
* to write an XLOG_FPI_FOR_HINT WAL record to protect against torn pages.
* 2. The caller might have only share-lock instead of exclusive-lock on the
* buffer's content lock.
* 3. This function does not guarantee that the buffer is always marked dirty
* (due to a race condition), so it cannot be used for important changes.
*/
void
MarkBufferDirtyHint(Buffer buffer, bool buffer_std)
{
BufferDesc *bufHdr;
Page page = BufferGetPage(buffer);
if (!BufferIsValid(buffer))
elog(ERROR, "bad buffer ID: %d", buffer);
if (BufferIsLocal(buffer))
{
MarkLocalBufferDirty(buffer);
return;
}
bufHdr = GetBufferDescriptor(buffer - 1);
Assert(GetPrivateRefCount(buffer) > 0);
/* here, either share or exclusive lock is OK */
Assert(LWLockHeldByMe(BufferDescriptorGetContentLock(bufHdr)));
/*
* This routine might get called many times on the same page, if we are
* making the first scan after commit of an xact that added/deleted many
* tuples. So, be as quick as we can if the buffer is already dirty. We
* do this by not acquiring spinlock if it looks like the status bits are
* already set. Since we make this test unlocked, there's a chance we
* might fail to notice that the flags have just been cleared, and failed
* to reset them, due to memory-ordering issues. But since this function
* is only intended to be used in cases where failing to write out the
* data would be harmless anyway, it doesn't really matter.
*/
if ((pg_atomic_read_u32(&bufHdr->state) & (BM_DIRTY | BM_JUST_DIRTIED)) !=
(BM_DIRTY | BM_JUST_DIRTIED))
{
XLogRecPtr lsn = InvalidXLogRecPtr;
bool dirtied = false;
bool delayChkptFlags = false;
uint32 buf_state;
/*
* If we need to protect hint bit updates from torn writes, WAL-log a
* full page image of the page. This full page image is only necessary
* if the hint bit update is the first change to the page since the
* last checkpoint.
*
* We don't check full_page_writes here because that logic is included
* when we call XLogInsert() since the value changes dynamically.
*/
if (XLogHintBitIsNeeded() &&
(pg_atomic_read_u32(&bufHdr->state) & BM_PERMANENT))
{
/*
* If we must not write WAL, due to a relfilelocator-specific
* condition or being in recovery, don't dirty the page. We can
* set the hint, just not dirty the page as a result so the hint
* is lost when we evict the page or shutdown.
*
* See src/backend/storage/page/README for longer discussion.
*/
if (RecoveryInProgress() ||
RelFileLocatorSkippingWAL(BufTagGetRelFileLocator(&bufHdr->tag)))
return;
/*
* If the block is already dirty because we either made a change
* or set a hint already, then we don't need to write a full page
* image. Note that aggressive cleaning of blocks dirtied by hint
* bit setting would increase the call rate. Bulk setting of hint
* bits would reduce the call rate...
*
* We must issue the WAL record before we mark the buffer dirty.
* Otherwise we might write the page before we write the WAL. That
* causes a race condition, since a checkpoint might occur between
* writing the WAL record and marking the buffer dirty. We solve
* that with a kluge, but one that is already in use during
* transaction commit to prevent race conditions. Basically, we
* simply prevent the checkpoint WAL record from being written
* until we have marked the buffer dirty. We don't start the
* checkpoint flush until we have marked dirty, so our checkpoint
* must flush the change to disk successfully or the checkpoint
* never gets written, so crash recovery will fix.
*
* It's possible we may enter here without an xid, so it is
* essential that CreateCheckPoint waits for virtual transactions
* rather than full transactionids.
*/
Assert((MyProc->delayChkptFlags & DELAY_CHKPT_START) == 0);
MyProc->delayChkptFlags |= DELAY_CHKPT_START;
delayChkptFlags = true;
lsn = XLogSaveBufferForHint(buffer, buffer_std);
}
buf_state = LockBufHdr(bufHdr);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
if (!(buf_state & BM_DIRTY))
{
dirtied = true; /* Means "will be dirtied by this action" */
/*
* Set the page LSN if we wrote a backup block. We aren't supposed
* to set this when only holding a share lock but as long as we
* serialise it somehow we're OK. We choose to set LSN while
* holding the buffer header lock, which causes any reader of an
* LSN who holds only a share lock to also obtain a buffer header
* lock before using PageGetLSN(), which is enforced in
* BufferGetLSNAtomic().
*
* If checksums are enabled, you might think we should reset the
* checksum here. That will happen when the page is written
* sometime later in this checkpoint cycle.
*/
if (!XLogRecPtrIsInvalid(lsn))
PageSetLSN(page, lsn);
}
buf_state |= BM_DIRTY | BM_JUST_DIRTIED;
UnlockBufHdr(bufHdr, buf_state);
if (delayChkptFlags)
MyProc->delayChkptFlags &= ~DELAY_CHKPT_START;
if (dirtied)
{
pgBufferUsage.shared_blks_dirtied++;
if (VacuumCostActive)
VacuumCostBalance += VacuumCostPageDirty;
}
}
}
/*
* Release buffer content locks for shared buffers.
*
* Used to clean up after errors.
*
* Currently, we can expect that lwlock.c's LWLockReleaseAll() took care
* of releasing buffer content locks per se; the only thing we need to deal
* with here is clearing any PIN_COUNT request that was in progress.
*/
void
UnlockBuffers(void)
{
BufferDesc *buf = PinCountWaitBuf;
if (buf)
{
uint32 buf_state;
buf_state = LockBufHdr(buf);
/*
* Don't complain if flag bit not set; it could have been reset but we
* got a cancel/die interrupt before getting the signal.
*/
if ((buf_state & BM_PIN_COUNT_WAITER) != 0 &&
buf->wait_backend_pgprocno == MyProcNumber)
buf_state &= ~BM_PIN_COUNT_WAITER;
UnlockBufHdr(buf, buf_state);
PinCountWaitBuf = NULL;
}
}
/*
* Acquire or release the content_lock for the buffer.
*/
void
LockBuffer(Buffer buffer, int mode)
{
BufferDesc *buf;
Assert(BufferIsPinned(buffer));
if (BufferIsLocal(buffer))
return; /* local buffers need no lock */
buf = GetBufferDescriptor(buffer - 1);
if (mode == BUFFER_LOCK_UNLOCK)
LWLockRelease(BufferDescriptorGetContentLock(buf));
else if (mode == BUFFER_LOCK_SHARE)
LWLockAcquire(BufferDescriptorGetContentLock(buf), LW_SHARED);
else if (mode == BUFFER_LOCK_EXCLUSIVE)
LWLockAcquire(BufferDescriptorGetContentLock(buf), LW_EXCLUSIVE);
else
elog(ERROR, "unrecognized buffer lock mode: %d", mode);
}
/*
* Acquire the content_lock for the buffer, but only if we don't have to wait.
*
* This assumes the caller wants BUFFER_LOCK_EXCLUSIVE mode.
*/
bool
ConditionalLockBuffer(Buffer buffer)
{
BufferDesc *buf;
Assert(BufferIsPinned(buffer));
if (BufferIsLocal(buffer))
return true; /* act as though we got it */
buf = GetBufferDescriptor(buffer - 1);
return LWLockConditionalAcquire(BufferDescriptorGetContentLock(buf),
LW_EXCLUSIVE);
}
/*
* Verify that this backend is pinning the buffer exactly once.
*
* NOTE: Like in BufferIsPinned(), what we check here is that *this* backend
* holds a pin on the buffer. We do not care whether some other backend does.
*/
void
CheckBufferIsPinnedOnce(Buffer buffer)
{
if (BufferIsLocal(buffer))
{
if (LocalRefCount[-buffer - 1] != 1)
elog(ERROR, "incorrect local pin count: %d",
LocalRefCount[-buffer - 1]);
}
else
{
if (GetPrivateRefCount(buffer) != 1)
elog(ERROR, "incorrect local pin count: %d",
GetPrivateRefCount(buffer));
}
}
/*
* LockBufferForCleanup - lock a buffer in preparation for deleting items
*
* Items may be deleted from a disk page only when the caller (a) holds an
* exclusive lock on the buffer and (b) has observed that no other backend
* holds a pin on the buffer. If there is a pin, then the other backend
* might have a pointer into the buffer (for example, a heapscan reference
* to an item --- see README for more details). It's OK if a pin is added
* after the cleanup starts, however; the newly-arrived backend will be
* unable to look at the page until we release the exclusive lock.
*
* To implement this protocol, a would-be deleter must pin the buffer and
* then call LockBufferForCleanup(). LockBufferForCleanup() is similar to
* LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE), except that it loops until
* it has successfully observed pin count = 1.
*/
void
LockBufferForCleanup(Buffer buffer)
{
BufferDesc *bufHdr;
TimestampTz waitStart = 0;
bool waiting = false;
bool logged_recovery_conflict = false;
Assert(BufferIsPinned(buffer));
Assert(PinCountWaitBuf == NULL);
CheckBufferIsPinnedOnce(buffer);
/* Nobody else to wait for */
if (BufferIsLocal(buffer))
return;
bufHdr = GetBufferDescriptor(buffer - 1);
for (;;)
{
uint32 buf_state;
/* Try to acquire lock */
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
buf_state = LockBufHdr(bufHdr);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
if (BUF_STATE_GET_REFCOUNT(buf_state) == 1)
{
/* Successfully acquired exclusive lock with pincount 1 */
UnlockBufHdr(bufHdr, buf_state);
/*
* Emit the log message if recovery conflict on buffer pin was
* resolved but the startup process waited longer than
* deadlock_timeout for it.
*/
if (logged_recovery_conflict)
LogRecoveryConflict(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
waitStart, GetCurrentTimestamp(),
NULL, false);
if (waiting)
{
/* reset ps display to remove the suffix if we added one */
set_ps_display_remove_suffix();
waiting = false;
}
return;
}
/* Failed, so mark myself as waiting for pincount 1 */
if (buf_state & BM_PIN_COUNT_WAITER)
{
UnlockBufHdr(bufHdr, buf_state);
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
elog(ERROR, "multiple backends attempting to wait for pincount 1");
}
bufHdr->wait_backend_pgprocno = MyProcNumber;
PinCountWaitBuf = bufHdr;
buf_state |= BM_PIN_COUNT_WAITER;
UnlockBufHdr(bufHdr, buf_state);
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
/* Wait to be signaled by UnpinBuffer() */
if (InHotStandby)
{
if (!waiting)
{
/* adjust the process title to indicate that it's waiting */
set_ps_display_suffix("waiting");
waiting = true;
}
/*
* Emit the log message if the startup process is waiting longer
* than deadlock_timeout for recovery conflict on buffer pin.
*
* Skip this if first time through because the startup process has
* not started waiting yet in this case. So, the wait start
* timestamp is set after this logic.
*/
if (waitStart != 0 && !logged_recovery_conflict)
{
TimestampTz now = GetCurrentTimestamp();
if (TimestampDifferenceExceeds(waitStart, now,
DeadlockTimeout))
{
LogRecoveryConflict(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
waitStart, now, NULL, true);
logged_recovery_conflict = true;
}
}
/*
* Set the wait start timestamp if logging is enabled and first
* time through.
*/
if (log_recovery_conflict_waits && waitStart == 0)
waitStart = GetCurrentTimestamp();
/* Publish the bufid that Startup process waits on */
SetStartupBufferPinWaitBufId(buffer - 1);
/* Set alarm and then wait to be signaled by UnpinBuffer() */
ResolveRecoveryConflictWithBufferPin();
/* Reset the published bufid */
SetStartupBufferPinWaitBufId(-1);
}
else
ProcWaitForSignal(WAIT_EVENT_BUFFER_PIN);
/*
* Remove flag marking us as waiter. Normally this will not be set
* anymore, but ProcWaitForSignal() can return for other signals as
* well. We take care to only reset the flag if we're the waiter, as
* theoretically another backend could have started waiting. That's
* impossible with the current usages due to table level locking, but
* better be safe.
*/
buf_state = LockBufHdr(bufHdr);
if ((buf_state & BM_PIN_COUNT_WAITER) != 0 &&
bufHdr->wait_backend_pgprocno == MyProcNumber)
buf_state &= ~BM_PIN_COUNT_WAITER;
UnlockBufHdr(bufHdr, buf_state);
PinCountWaitBuf = NULL;
/* Loop back and try again */
}
}
/*
* Check called from ProcessRecoveryConflictInterrupts() when Startup process
* requests cancellation of all pin holders that are blocking it.
*/
bool
HoldingBufferPinThatDelaysRecovery(void)
{
int bufid = GetStartupBufferPinWaitBufId();
/*
* If we get woken slowly then it's possible that the Startup process was
* already woken by other backends before we got here. Also possible that
* we get here by multiple interrupts or interrupts at inappropriate
* times, so make sure we do nothing if the bufid is not set.
*/
if (bufid < 0)
return false;
if (GetPrivateRefCount(bufid + 1) > 0)
return true;
return false;
}
/*
* ConditionalLockBufferForCleanup - as above, but don't wait to get the lock
*
* We won't loop, but just check once to see if the pin count is OK. If
* not, return false with no lock held.
*/
bool
ConditionalLockBufferForCleanup(Buffer buffer)
{
BufferDesc *bufHdr;
uint32 buf_state,
refcount;
Assert(BufferIsValid(buffer));
if (BufferIsLocal(buffer))
{
refcount = LocalRefCount[-buffer - 1];
/* There should be exactly one pin */
Assert(refcount > 0);
if (refcount != 1)
return false;
/* Nobody else to wait for */
return true;
}
/* There should be exactly one local pin */
refcount = GetPrivateRefCount(buffer);
Assert(refcount);
if (refcount != 1)
return false;
/* Try to acquire lock */
if (!ConditionalLockBuffer(buffer))
return false;
bufHdr = GetBufferDescriptor(buffer - 1);
buf_state = LockBufHdr(bufHdr);
refcount = BUF_STATE_GET_REFCOUNT(buf_state);
Assert(refcount > 0);
if (refcount == 1)
{
/* Successfully acquired exclusive lock with pincount 1 */
UnlockBufHdr(bufHdr, buf_state);
return true;
}
/* Failed, so release the lock */
UnlockBufHdr(bufHdr, buf_state);
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
return false;
}
/*
* IsBufferCleanupOK - as above, but we already have the lock
*
* Check whether it's OK to perform cleanup on a buffer we've already
* locked. If we observe that the pin count is 1, our exclusive lock
* happens to be a cleanup lock, and we can proceed with anything that
* would have been allowable had we sought a cleanup lock originally.
*/
bool
IsBufferCleanupOK(Buffer buffer)
{
BufferDesc *bufHdr;
uint32 buf_state;
Assert(BufferIsValid(buffer));
if (BufferIsLocal(buffer))
{
/* There should be exactly one pin */
if (LocalRefCount[-buffer - 1] != 1)
return false;
/* Nobody else to wait for */
return true;
}
/* There should be exactly one local pin */
if (GetPrivateRefCount(buffer) != 1)
return false;
bufHdr = GetBufferDescriptor(buffer - 1);
/* caller must hold exclusive lock on buffer */
Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
LW_EXCLUSIVE));
buf_state = LockBufHdr(bufHdr);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
if (BUF_STATE_GET_REFCOUNT(buf_state) == 1)
{
/* pincount is OK. */
UnlockBufHdr(bufHdr, buf_state);
return true;
}
UnlockBufHdr(bufHdr, buf_state);
return false;
}
/*
* Functions for buffer I/O handling
*
* Note: We assume that nested buffer I/O never occurs.
* i.e at most one BM_IO_IN_PROGRESS bit is set per proc.
*
* Also note that these are used only for shared buffers, not local ones.
*/
/*
* WaitIO -- Block until the IO_IN_PROGRESS flag on 'buf' is cleared.
*/
static void
WaitIO(BufferDesc *buf)
{
ConditionVariable *cv = BufferDescriptorGetIOCV(buf);
ConditionVariablePrepareToSleep(cv);
for (;;)
{
uint32 buf_state;
/*
* It may not be necessary to acquire the spinlock to check the flag
* here, but since this test is essential for correctness, we'd better
* play it safe.
*/
buf_state = LockBufHdr(buf);
UnlockBufHdr(buf, buf_state);
if (!(buf_state & BM_IO_IN_PROGRESS))
break;
ConditionVariableSleep(cv, WAIT_EVENT_BUFFER_IO);
}
ConditionVariableCancelSleep();
}
/*
* StartBufferIO: begin I/O on this buffer
* (Assumptions)
* My process is executing no IO
* The buffer is Pinned
*
* In some scenarios there are race conditions in which multiple backends
* could attempt the same I/O operation concurrently. If someone else
* has already started I/O on this buffer then we will block on the
* I/O condition variable until he's done.
*
* Input operations are only attempted on buffers that are not BM_VALID,
* and output operations only on buffers that are BM_VALID and BM_DIRTY,
* so we can always tell if the work is already done.
*
* Returns true if we successfully marked the buffer as I/O busy,
* false if someone else already did the work.
*
* If nowait is true, then we don't wait for an I/O to be finished by another
* backend. In that case, false indicates either that the I/O was already
* finished, or is still in progress. This is useful for callers that want to
* find out if they can perform the I/O as part of a larger operation, without
* waiting for the answer or distinguishing the reasons why not.
*/
static bool
StartBufferIO(BufferDesc *buf, bool forInput, bool nowait)
{
uint32 buf_state;
ResourceOwnerEnlarge(CurrentResourceOwner);
for (;;)
{
buf_state = LockBufHdr(buf);
if (!(buf_state & BM_IO_IN_PROGRESS))
break;
UnlockBufHdr(buf, buf_state);
if (nowait)
return false;
WaitIO(buf);
}
/* Once we get here, there is definitely no I/O active on this buffer */
if (forInput ? (buf_state & BM_VALID) : !(buf_state & BM_DIRTY))
{
/* someone else already did the I/O */
UnlockBufHdr(buf, buf_state);
return false;
}
buf_state |= BM_IO_IN_PROGRESS;
UnlockBufHdr(buf, buf_state);
ResourceOwnerRememberBufferIO(CurrentResourceOwner,
BufferDescriptorGetBuffer(buf));
return true;
}
/*
* TerminateBufferIO: release a buffer we were doing I/O on
* (Assumptions)
* My process is executing IO for the buffer
* BM_IO_IN_PROGRESS bit is set for the buffer
* The buffer is Pinned
*
* If clear_dirty is true and BM_JUST_DIRTIED is not set, we clear the
* buffer's BM_DIRTY flag. This is appropriate when terminating a
* successful write. The check on BM_JUST_DIRTIED is necessary to avoid
* marking the buffer clean if it was re-dirtied while we were writing.
*
* set_flag_bits gets ORed into the buffer's flags. It must include
* BM_IO_ERROR in a failure case. For successful completion it could
* be 0, or BM_VALID if we just finished reading in the page.
*
* If forget_owner is true, we release the buffer I/O from the current
* resource owner. (forget_owner=false is used when the resource owner itself
* is being released)
*/
static void
TerminateBufferIO(BufferDesc *buf, bool clear_dirty, uint32 set_flag_bits,
bool forget_owner)
{
uint32 buf_state;
buf_state = LockBufHdr(buf);
Assert(buf_state & BM_IO_IN_PROGRESS);
buf_state &= ~(BM_IO_IN_PROGRESS | BM_IO_ERROR);
if (clear_dirty && !(buf_state & BM_JUST_DIRTIED))
buf_state &= ~(BM_DIRTY | BM_CHECKPOINT_NEEDED);
buf_state |= set_flag_bits;
UnlockBufHdr(buf, buf_state);
if (forget_owner)
ResourceOwnerForgetBufferIO(CurrentResourceOwner,
BufferDescriptorGetBuffer(buf));
ConditionVariableBroadcast(BufferDescriptorGetIOCV(buf));
}
/*
* AbortBufferIO: Clean up active buffer I/O after an error.
*
* All LWLocks we might have held have been released,
* but we haven't yet released buffer pins, so the buffer is still pinned.
*
* If I/O was in progress, we always set BM_IO_ERROR, even though it's
* possible the error condition wasn't related to the I/O.
*
* Note: this does not remove the buffer I/O from the resource owner.
* That's correct when we're releasing the whole resource owner, but
* beware if you use this in other contexts.
*/
static void
AbortBufferIO(Buffer buffer)
{
BufferDesc *buf_hdr = GetBufferDescriptor(buffer - 1);
uint32 buf_state;
buf_state = LockBufHdr(buf_hdr);
Assert(buf_state & (BM_IO_IN_PROGRESS | BM_TAG_VALID));
if (!(buf_state & BM_VALID))
{
Assert(!(buf_state & BM_DIRTY));
UnlockBufHdr(buf_hdr, buf_state);
}
else
{
Assert(buf_state & BM_DIRTY);
UnlockBufHdr(buf_hdr, buf_state);
/* Issue notice if this is not the first failure... */
if (buf_state & BM_IO_ERROR)
{
/* Buffer is pinned, so we can read tag without spinlock */
char *path;
path = relpathperm(BufTagGetRelFileLocator(&buf_hdr->tag),
BufTagGetForkNum(&buf_hdr->tag));
ereport(WARNING,
(errcode(ERRCODE_IO_ERROR),
errmsg("could not write block %u of %s",
buf_hdr->tag.blockNum, path),
errdetail("Multiple failures --- write error might be permanent.")));
pfree(path);
}
}
TerminateBufferIO(buf_hdr, false, BM_IO_ERROR, false);
}
/*
* Error context callback for errors occurring during shared buffer writes.
*/
static void
shared_buffer_write_error_callback(void *arg)
{
BufferDesc *bufHdr = (BufferDesc *) arg;
/* Buffer is pinned, so we can read the tag without locking the spinlock */
if (bufHdr != NULL)
{
char *path = relpathperm(BufTagGetRelFileLocator(&bufHdr->tag),
BufTagGetForkNum(&bufHdr->tag));
errcontext("writing block %u of relation %s",
bufHdr->tag.blockNum, path);
pfree(path);
}
}
/*
* Error context callback for errors occurring during local buffer writes.
*/
static void
local_buffer_write_error_callback(void *arg)
{
BufferDesc *bufHdr = (BufferDesc *) arg;
if (bufHdr != NULL)
{
char *path = relpathbackend(BufTagGetRelFileLocator(&bufHdr->tag),
MyProcNumber,
BufTagGetForkNum(&bufHdr->tag));
errcontext("writing block %u of relation %s",
bufHdr->tag.blockNum, path);
pfree(path);
}
}
/*
* RelFileLocator qsort/bsearch comparator; see RelFileLocatorEquals.
*/
static int
rlocator_comparator(const void *p1, const void *p2)
{
RelFileLocator n1 = *(const RelFileLocator *) p1;
RelFileLocator n2 = *(const RelFileLocator *) p2;
if (n1.relNumber < n2.relNumber)
return -1;
else if (n1.relNumber > n2.relNumber)
return 1;
if (n1.dbOid < n2.dbOid)
return -1;
else if (n1.dbOid > n2.dbOid)
return 1;
if (n1.spcOid < n2.spcOid)
return -1;
else if (n1.spcOid > n2.spcOid)
return 1;
else
return 0;
}
/*
* Lock buffer header - set BM_LOCKED in buffer state.
*/
uint32
LockBufHdr(BufferDesc *desc)
{
SpinDelayStatus delayStatus;
uint32 old_buf_state;
Assert(!BufferIsLocal(BufferDescriptorGetBuffer(desc)));
init_local_spin_delay(&delayStatus);
while (true)
{
/* set BM_LOCKED flag */
old_buf_state = pg_atomic_fetch_or_u32(&desc->state, BM_LOCKED);
/* if it wasn't set before we're OK */
if (!(old_buf_state & BM_LOCKED))
break;
perform_spin_delay(&delayStatus);
}
finish_spin_delay(&delayStatus);
return old_buf_state | BM_LOCKED;
}
/*
* Wait until the BM_LOCKED flag isn't set anymore and return the buffer's
* state at that point.
*
* Obviously the buffer could be locked by the time the value is returned, so
* this is primarily useful in CAS style loops.
*/
static uint32
WaitBufHdrUnlocked(BufferDesc *buf)
{
SpinDelayStatus delayStatus;
uint32 buf_state;
init_local_spin_delay(&delayStatus);
buf_state = pg_atomic_read_u32(&buf->state);
while (buf_state & BM_LOCKED)
{
perform_spin_delay(&delayStatus);
buf_state = pg_atomic_read_u32(&buf->state);
}
finish_spin_delay(&delayStatus);
return buf_state;
}
/*
* BufferTag comparator.
*/
static inline int
buffertag_comparator(const BufferTag *ba, const BufferTag *bb)
{
int ret;
RelFileLocator rlocatora;
RelFileLocator rlocatorb;
rlocatora = BufTagGetRelFileLocator(ba);
rlocatorb = BufTagGetRelFileLocator(bb);
ret = rlocator_comparator(&rlocatora, &rlocatorb);
if (ret != 0)
return ret;
if (BufTagGetForkNum(ba) < BufTagGetForkNum(bb))
return -1;
if (BufTagGetForkNum(ba) > BufTagGetForkNum(bb))
return 1;
if (ba->blockNum < bb->blockNum)
return -1;
if (ba->blockNum > bb->blockNum)
return 1;
return 0;
}
/*
* Comparator determining the writeout order in a checkpoint.
*
* It is important that tablespaces are compared first, the logic balancing
* writes between tablespaces relies on it.
*/
static inline int
ckpt_buforder_comparator(const CkptSortItem *a, const CkptSortItem *b)
{
/* compare tablespace */
if (a->tsId < b->tsId)
return -1;
else if (a->tsId > b->tsId)
return 1;
/* compare relation */
if (a->relNumber < b->relNumber)
return -1;
else if (a->relNumber > b->relNumber)
return 1;
/* compare fork */
else if (a->forkNum < b->forkNum)
return -1;
else if (a->forkNum > b->forkNum)
return 1;
/* compare block number */
else if (a->blockNum < b->blockNum)
return -1;
else if (a->blockNum > b->blockNum)
return 1;
/* equal page IDs are unlikely, but not impossible */
return 0;
}
/*
* Comparator for a Min-Heap over the per-tablespace checkpoint completion
* progress.
*/
static int
ts_ckpt_progress_comparator(Datum a, Datum b, void *arg)
{
CkptTsStatus *sa = (CkptTsStatus *) a;
CkptTsStatus *sb = (CkptTsStatus *) b;
/* we want a min-heap, so return 1 for the a < b */
if (sa->progress < sb->progress)
return 1;
else if (sa->progress == sb->progress)
return 0;
else
return -1;
}
/*
* Initialize a writeback context, discarding potential previous state.
*
* *max_pending is a pointer instead of an immediate value, so the coalesce
* limits can easily changed by the GUC mechanism, and so calling code does
* not have to check the current configuration. A value of 0 means that no
* writeback control will be performed.
*/
void
WritebackContextInit(WritebackContext *context, int *max_pending)
{
Assert(*max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
context->max_pending = max_pending;
context->nr_pending = 0;
}
/*
* Add buffer to list of pending writeback requests.
*/
void
ScheduleBufferTagForWriteback(WritebackContext *wb_context, IOContext io_context,
BufferTag *tag)
{
PendingWriteback *pending;
/*
* As pg_flush_data() doesn't do anything with fsync disabled, there's no
* point in tracking in that case.
*/
if (io_direct_flags & IO_DIRECT_DATA ||
!enableFsync)
return;
/*
* Add buffer to the pending writeback array, unless writeback control is
* disabled.
*/
if (*wb_context->max_pending > 0)
{
Assert(*wb_context->max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
pending = &wb_context->pending_writebacks[wb_context->nr_pending++];
pending->tag = *tag;
}
/*
* Perform pending flushes if the writeback limit is exceeded. This
* includes the case where previously an item has been added, but control
* is now disabled.
*/
if (wb_context->nr_pending >= *wb_context->max_pending)
IssuePendingWritebacks(wb_context, io_context);
}
#define ST_SORT sort_pending_writebacks
#define ST_ELEMENT_TYPE PendingWriteback
#define ST_COMPARE(a, b) buffertag_comparator(&a->tag, &b->tag)
#define ST_SCOPE static
#define ST_DEFINE
#include <lib/sort_template.h>
/*
* Issue all pending writeback requests, previously scheduled with
* ScheduleBufferTagForWriteback, to the OS.
*
* Because this is only used to improve the OSs IO scheduling we try to never
* error out - it's just a hint.
*/
void
IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
{
instr_time io_start;
int i;
if (wb_context->nr_pending == 0)
return;
/*
* Executing the writes in-order can make them a lot faster, and allows to
* merge writeback requests to consecutive blocks into larger writebacks.
*/
sort_pending_writebacks(wb_context->pending_writebacks,
wb_context->nr_pending);
io_start = pgstat_prepare_io_time(track_io_timing);
/*
* Coalesce neighbouring writes, but nothing else. For that we iterate
* through the, now sorted, array of pending flushes, and look forward to
* find all neighbouring (or identical) writes.
*/
for (i = 0; i < wb_context->nr_pending; i++)
{
PendingWriteback *cur;
PendingWriteback *next;
SMgrRelation reln;
int ahead;
BufferTag tag;
RelFileLocator currlocator;
Size nblocks = 1;
cur = &wb_context->pending_writebacks[i];
tag = cur->tag;
currlocator = BufTagGetRelFileLocator(&tag);
/*
* Peek ahead, into following writeback requests, to see if they can
* be combined with the current one.
*/
for (ahead = 0; i + ahead + 1 < wb_context->nr_pending; ahead++)
{
next = &wb_context->pending_writebacks[i + ahead + 1];
/* different file, stop */
if (!RelFileLocatorEquals(currlocator,
BufTagGetRelFileLocator(&next->tag)) ||
BufTagGetForkNum(&cur->tag) != BufTagGetForkNum(&next->tag))
break;
/* ok, block queued twice, skip */
if (cur->tag.blockNum == next->tag.blockNum)
continue;
/* only merge consecutive writes */
if (cur->tag.blockNum + 1 != next->tag.blockNum)
break;
nblocks++;
cur = next;
}
i += ahead;
/* and finally tell the kernel to write the data to storage */
reln = smgropen(currlocator, INVALID_PROC_NUMBER);
smgrwriteback(reln, BufTagGetForkNum(&tag), tag.blockNum, nblocks);
}
/*
* Assume that writeback requests are only issued for buffers containing
* blocks of permanent relations.
*/
pgstat_count_io_op_time(IOOBJECT_RELATION, io_context,
IOOP_WRITEBACK, io_start, wb_context->nr_pending);
wb_context->nr_pending = 0;
}
/* ResourceOwner callbacks */
static void
ResOwnerReleaseBufferIO(Datum res)
{
Buffer buffer = DatumGetInt32(res);
AbortBufferIO(buffer);
}
static char *
ResOwnerPrintBufferIO(Datum res)
{
Buffer buffer = DatumGetInt32(res);
return psprintf("lost track of buffer IO on buffer %d", buffer);
}
static void
ResOwnerReleaseBufferPin(Datum res)
{
Buffer buffer = DatumGetInt32(res);
/* Like ReleaseBuffer, but don't call ResourceOwnerForgetBuffer */
if (!BufferIsValid(buffer))
elog(ERROR, "bad buffer ID: %d", buffer);
if (BufferIsLocal(buffer))
UnpinLocalBufferNoOwner(buffer);
else
UnpinBufferNoOwner(GetBufferDescriptor(buffer - 1));
}
static char *
ResOwnerPrintBufferPin(Datum res)
{
return DebugPrintBufferRefcount(DatumGetInt32(res));
}
/*
* Try to evict the current block in a shared buffer.
*
* This function is intended for testing/development use only!
*
* To succeed, the buffer must not be pinned on entry, so if the caller had a
* particular block in mind, it might already have been replaced by some other
* block by the time this function runs. It's also unpinned on return, so the
* buffer might be occupied again by the time control is returned, potentially
* even by the same block. This inherent raciness without other interlocking
* makes the function unsuitable for non-testing usage.
*
* Returns true if the buffer was valid and it has now been made invalid.
* Returns false if it wasn't valid, if it couldn't be evicted due to a pin,
* or if the buffer becomes dirty again while we're trying to write it out.
*/
bool
EvictUnpinnedBuffer(Buffer buf)
{
BufferDesc *desc;
uint32 buf_state;
bool result;
/* Make sure we can pin the buffer. */
ResourceOwnerEnlarge(CurrentResourceOwner);
ReservePrivateRefCountEntry();
Assert(!BufferIsLocal(buf));
desc = GetBufferDescriptor(buf - 1);
/* Lock the header and check if it's valid. */
buf_state = LockBufHdr(desc);
if ((buf_state & BM_VALID) == 0)
{
UnlockBufHdr(desc, buf_state);
return false;
}
/* Check that it's not pinned already. */
if (BUF_STATE_GET_REFCOUNT(buf_state) > 0)
{
UnlockBufHdr(desc, buf_state);
return false;
}
PinBuffer_Locked(desc); /* releases spinlock */
/* If it was dirty, try to clean it once. */
if (buf_state & BM_DIRTY)
{
LWLockAcquire(BufferDescriptorGetContentLock(desc), LW_SHARED);
FlushBuffer(desc, NULL, IOOBJECT_RELATION, IOCONTEXT_NORMAL);
LWLockRelease(BufferDescriptorGetContentLock(desc));
}
/* This will return false if it becomes dirty or someone else pins it. */
result = InvalidateVictimBuffer(desc);
UnpinBuffer(desc);
return result;
}