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866e24d47d
Mark Dilger, reviewed by Peter Geoghegan, Andres Freund, Álvaro Herrera, Michael Paquier, Amul Sul, and by me. Some last-minute cosmetic revisions by me. Discussion: http://postgr.es/m/12ED3DA8-25F0-4B68-937D-D907CFBF08E7@enterprisedb.com
3415 lines
110 KiB
C
3415 lines
110 KiB
C
/*-------------------------------------------------------------------------
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*
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* multixact.c
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* PostgreSQL multi-transaction-log manager
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*
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* The pg_multixact manager is a pg_xact-like manager that stores an array of
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* MultiXactMember for each MultiXactId. It is a fundamental part of the
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* shared-row-lock implementation. Each MultiXactMember is comprised of a
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* TransactionId and a set of flag bits. The name is a bit historical:
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* originally, a MultiXactId consisted of more than one TransactionId (except
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* in rare corner cases), hence "multi". Nowadays, however, it's perfectly
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* legitimate to have MultiXactIds that only include a single Xid.
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*
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* The meaning of the flag bits is opaque to this module, but they are mostly
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* used in heapam.c to identify lock modes that each of the member transactions
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* is holding on any given tuple. This module just contains support to store
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* and retrieve the arrays.
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*
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* We use two SLRU areas, one for storing the offsets at which the data
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* starts for each MultiXactId in the other one. This trick allows us to
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* store variable length arrays of TransactionIds. (We could alternatively
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* use one area containing counts and TransactionIds, with valid MultiXactId
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* values pointing at slots containing counts; but that way seems less robust
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* since it would get completely confused if someone inquired about a bogus
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* MultiXactId that pointed to an intermediate slot containing an XID.)
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*
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* XLOG interactions: this module generates a record whenever a new OFFSETs or
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* MEMBERs page is initialized to zeroes, as well as an
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* XLOG_MULTIXACT_CREATE_ID record whenever a new MultiXactId is defined.
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* This module ignores the WAL rule "write xlog before data," because it
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* suffices that actions recording a MultiXactId in a heap xmax do follow that
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* rule. The only way for the MXID to be referenced from any data page is for
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* heap_lock_tuple() or heap_update() to have put it there, and each generates
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* an XLOG record that must follow ours. The normal LSN interlock between the
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* data page and that XLOG record will ensure that our XLOG record reaches
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* disk first. If the SLRU members/offsets data reaches disk sooner than the
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* XLOG records, we do not care; after recovery, no xmax will refer to it. On
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* the flip side, to ensure that all referenced entries _do_ reach disk, this
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* module's XLOG records completely rebuild the data entered since the last
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* checkpoint. We flush and sync all dirty OFFSETs and MEMBERs pages to disk
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* before each checkpoint is considered complete.
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*
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* Like clog.c, and unlike subtrans.c, we have to preserve state across
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* crashes and ensure that MXID and offset numbering increases monotonically
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* across a crash. We do this in the same way as it's done for transaction
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* IDs: the WAL record is guaranteed to contain evidence of every MXID we
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* could need to worry about, and we just make sure that at the end of
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* replay, the next-MXID and next-offset counters are at least as large as
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* anything we saw during replay.
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*
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* We are able to remove segments no longer necessary by carefully tracking
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* each table's used values: during vacuum, any multixact older than a certain
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* value is removed; the cutoff value is stored in pg_class. The minimum value
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* across all tables in each database is stored in pg_database, and the global
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* minimum across all databases is part of pg_control and is kept in shared
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* memory. Whenever that minimum is advanced, the SLRUs are truncated.
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*
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* When new multixactid values are to be created, care is taken that the
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* counter does not fall within the wraparound horizon considering the global
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* minimum value.
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*
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* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/backend/access/transam/multixact.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/multixact.h"
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#include "access/slru.h"
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#include "access/transam.h"
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#include "access/twophase.h"
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#include "access/twophase_rmgr.h"
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#include "access/xact.h"
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#include "access/xlog.h"
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#include "access/xloginsert.h"
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#include "catalog/pg_type.h"
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#include "commands/dbcommands.h"
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#include "funcapi.h"
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#include "lib/ilist.h"
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#include "miscadmin.h"
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#include "pg_trace.h"
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#include "postmaster/autovacuum.h"
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#include "storage/lmgr.h"
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#include "storage/pmsignal.h"
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#include "storage/proc.h"
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#include "storage/procarray.h"
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#include "utils/builtins.h"
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#include "utils/memutils.h"
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#include "utils/snapmgr.h"
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/*
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* Defines for MultiXactOffset page sizes. A page is the same BLCKSZ as is
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* used everywhere else in Postgres.
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*
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* Note: because MultiXactOffsets are 32 bits and wrap around at 0xFFFFFFFF,
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* MultiXact page numbering also wraps around at
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* 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE, and segment numbering at
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* 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need
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* take no explicit notice of that fact in this module, except when comparing
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* segment and page numbers in TruncateMultiXact (see
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* MultiXactOffsetPagePrecedes).
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*/
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/* We need four bytes per offset */
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#define MULTIXACT_OFFSETS_PER_PAGE (BLCKSZ / sizeof(MultiXactOffset))
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#define MultiXactIdToOffsetPage(xid) \
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((xid) / (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
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#define MultiXactIdToOffsetEntry(xid) \
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((xid) % (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
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#define MultiXactIdToOffsetSegment(xid) (MultiXactIdToOffsetPage(xid) / SLRU_PAGES_PER_SEGMENT)
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/*
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* The situation for members is a bit more complex: we store one byte of
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* additional flag bits for each TransactionId. To do this without getting
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* into alignment issues, we store four bytes of flags, and then the
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* corresponding 4 Xids. Each such 5-word (20-byte) set we call a "group", and
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* are stored as a whole in pages. Thus, with 8kB BLCKSZ, we keep 409 groups
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* per page. This wastes 12 bytes per page, but that's OK -- simplicity (and
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* performance) trumps space efficiency here.
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*
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* Note that the "offset" macros work with byte offset, not array indexes, so
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* arithmetic must be done using "char *" pointers.
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*/
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/* We need eight bits per xact, so one xact fits in a byte */
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#define MXACT_MEMBER_BITS_PER_XACT 8
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#define MXACT_MEMBER_FLAGS_PER_BYTE 1
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#define MXACT_MEMBER_XACT_BITMASK ((1 << MXACT_MEMBER_BITS_PER_XACT) - 1)
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/* how many full bytes of flags are there in a group? */
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#define MULTIXACT_FLAGBYTES_PER_GROUP 4
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#define MULTIXACT_MEMBERS_PER_MEMBERGROUP \
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(MULTIXACT_FLAGBYTES_PER_GROUP * MXACT_MEMBER_FLAGS_PER_BYTE)
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/* size in bytes of a complete group */
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#define MULTIXACT_MEMBERGROUP_SIZE \
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(sizeof(TransactionId) * MULTIXACT_MEMBERS_PER_MEMBERGROUP + MULTIXACT_FLAGBYTES_PER_GROUP)
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#define MULTIXACT_MEMBERGROUPS_PER_PAGE (BLCKSZ / MULTIXACT_MEMBERGROUP_SIZE)
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#define MULTIXACT_MEMBERS_PER_PAGE \
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(MULTIXACT_MEMBERGROUPS_PER_PAGE * MULTIXACT_MEMBERS_PER_MEMBERGROUP)
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/*
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* Because the number of items per page is not a divisor of the last item
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* number (member 0xFFFFFFFF), the last segment does not use the maximum number
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* of pages, and moreover the last used page therein does not use the same
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* number of items as previous pages. (Another way to say it is that the
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* 0xFFFFFFFF member is somewhere in the middle of the last page, so the page
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* has some empty space after that item.)
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*
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* This constant is the number of members in the last page of the last segment.
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*/
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#define MAX_MEMBERS_IN_LAST_MEMBERS_PAGE \
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((uint32) ((0xFFFFFFFF % MULTIXACT_MEMBERS_PER_PAGE) + 1))
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/* page in which a member is to be found */
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#define MXOffsetToMemberPage(xid) ((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_PAGE)
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#define MXOffsetToMemberSegment(xid) (MXOffsetToMemberPage(xid) / SLRU_PAGES_PER_SEGMENT)
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/* Location (byte offset within page) of flag word for a given member */
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#define MXOffsetToFlagsOffset(xid) \
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((((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) % \
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(TransactionId) MULTIXACT_MEMBERGROUPS_PER_PAGE) * \
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(TransactionId) MULTIXACT_MEMBERGROUP_SIZE)
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#define MXOffsetToFlagsBitShift(xid) \
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(((xid) % (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) * \
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MXACT_MEMBER_BITS_PER_XACT)
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/* Location (byte offset within page) of TransactionId of given member */
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#define MXOffsetToMemberOffset(xid) \
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(MXOffsetToFlagsOffset(xid) + MULTIXACT_FLAGBYTES_PER_GROUP + \
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((xid) % MULTIXACT_MEMBERS_PER_MEMBERGROUP) * sizeof(TransactionId))
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/* Multixact members wraparound thresholds. */
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#define MULTIXACT_MEMBER_SAFE_THRESHOLD (MaxMultiXactOffset / 2)
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#define MULTIXACT_MEMBER_DANGER_THRESHOLD \
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(MaxMultiXactOffset - MaxMultiXactOffset / 4)
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#define PreviousMultiXactId(xid) \
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((xid) == FirstMultiXactId ? MaxMultiXactId : (xid) - 1)
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/*
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* Links to shared-memory data structures for MultiXact control
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*/
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static SlruCtlData MultiXactOffsetCtlData;
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static SlruCtlData MultiXactMemberCtlData;
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#define MultiXactOffsetCtl (&MultiXactOffsetCtlData)
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#define MultiXactMemberCtl (&MultiXactMemberCtlData)
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/*
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* MultiXact state shared across all backends. All this state is protected
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* by MultiXactGenLock. (We also use MultiXactOffsetSLRULock and
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* MultiXactMemberSLRULock to guard accesses to the two sets of SLRU
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* buffers. For concurrency's sake, we avoid holding more than one of these
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* locks at a time.)
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*/
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typedef struct MultiXactStateData
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{
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/* next-to-be-assigned MultiXactId */
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MultiXactId nextMXact;
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/* next-to-be-assigned offset */
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MultiXactOffset nextOffset;
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/* Have we completed multixact startup? */
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bool finishedStartup;
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/*
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* Oldest multixact that is still potentially referenced by a relation.
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* Anything older than this should not be consulted. These values are
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* updated by vacuum.
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*/
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MultiXactId oldestMultiXactId;
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Oid oldestMultiXactDB;
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/*
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* Oldest multixact offset that is potentially referenced by a multixact
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* referenced by a relation. We don't always know this value, so there's
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* a flag here to indicate whether or not we currently do.
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*/
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MultiXactOffset oldestOffset;
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bool oldestOffsetKnown;
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/* support for anti-wraparound measures */
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MultiXactId multiVacLimit;
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MultiXactId multiWarnLimit;
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MultiXactId multiStopLimit;
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MultiXactId multiWrapLimit;
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/* support for members anti-wraparound measures */
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MultiXactOffset offsetStopLimit; /* known if oldestOffsetKnown */
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/*
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* Per-backend data starts here. We have two arrays stored in the area
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* immediately following the MultiXactStateData struct. Each is indexed by
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* BackendId.
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*
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* In both arrays, there's a slot for all normal backends (1..MaxBackends)
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* followed by a slot for max_prepared_xacts prepared transactions. Valid
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* BackendIds start from 1; element zero of each array is never used.
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*
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* OldestMemberMXactId[k] is the oldest MultiXactId each backend's current
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* transaction(s) could possibly be a member of, or InvalidMultiXactId
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* when the backend has no live transaction that could possibly be a
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* member of a MultiXact. Each backend sets its entry to the current
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* nextMXact counter just before first acquiring a shared lock in a given
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* transaction, and clears it at transaction end. (This works because only
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* during or after acquiring a shared lock could an XID possibly become a
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* member of a MultiXact, and that MultiXact would have to be created
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* during or after the lock acquisition.)
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*
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* OldestVisibleMXactId[k] is the oldest MultiXactId each backend's
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* current transaction(s) think is potentially live, or InvalidMultiXactId
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* when not in a transaction or not in a transaction that's paid any
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* attention to MultiXacts yet. This is computed when first needed in a
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* given transaction, and cleared at transaction end. We can compute it
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* as the minimum of the valid OldestMemberMXactId[] entries at the time
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* we compute it (using nextMXact if none are valid). Each backend is
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* required not to attempt to access any SLRU data for MultiXactIds older
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* than its own OldestVisibleMXactId[] setting; this is necessary because
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* the checkpointer could truncate away such data at any instant.
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*
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* The oldest valid value among all of the OldestMemberMXactId[] and
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* OldestVisibleMXactId[] entries is considered by vacuum as the earliest
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* possible value still having any live member transaction. Subtracting
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* vacuum_multixact_freeze_min_age from that value we obtain the freezing
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* point for multixacts for that table. Any value older than that is
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* removed from tuple headers (or "frozen"; see FreezeMultiXactId. Note
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* that multis that have member xids that are older than the cutoff point
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* for xids must also be frozen, even if the multis themselves are newer
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* than the multixid cutoff point). Whenever a full table vacuum happens,
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* the freezing point so computed is used as the new pg_class.relminmxid
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* value. The minimum of all those values in a database is stored as
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* pg_database.datminmxid. In turn, the minimum of all of those values is
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* stored in pg_control and used as truncation point for pg_multixact. At
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* checkpoint or restartpoint, unneeded segments are removed.
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*/
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MultiXactId perBackendXactIds[FLEXIBLE_ARRAY_MEMBER];
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} MultiXactStateData;
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/*
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* Last element of OldestMemberMXactId and OldestVisibleMXactId arrays.
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* Valid elements are (1..MaxOldestSlot); element 0 is never used.
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*/
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#define MaxOldestSlot (MaxBackends + max_prepared_xacts)
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/* Pointers to the state data in shared memory */
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static MultiXactStateData *MultiXactState;
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static MultiXactId *OldestMemberMXactId;
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static MultiXactId *OldestVisibleMXactId;
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/*
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* Definitions for the backend-local MultiXactId cache.
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*
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* We use this cache to store known MultiXacts, so we don't need to go to
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* SLRU areas every time.
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*
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* The cache lasts for the duration of a single transaction, the rationale
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* for this being that most entries will contain our own TransactionId and
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* so they will be uninteresting by the time our next transaction starts.
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* (XXX not clear that this is correct --- other members of the MultiXact
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* could hang around longer than we did. However, it's not clear what a
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* better policy for flushing old cache entries would be.) FIXME actually
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* this is plain wrong now that multixact's may contain update Xids.
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*
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* We allocate the cache entries in a memory context that is deleted at
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* transaction end, so we don't need to do retail freeing of entries.
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*/
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typedef struct mXactCacheEnt
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{
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MultiXactId multi;
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int nmembers;
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dlist_node node;
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MultiXactMember members[FLEXIBLE_ARRAY_MEMBER];
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} mXactCacheEnt;
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#define MAX_CACHE_ENTRIES 256
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static dlist_head MXactCache = DLIST_STATIC_INIT(MXactCache);
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static int MXactCacheMembers = 0;
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static MemoryContext MXactContext = NULL;
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#ifdef MULTIXACT_DEBUG
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#define debug_elog2(a,b) elog(a,b)
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#define debug_elog3(a,b,c) elog(a,b,c)
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#define debug_elog4(a,b,c,d) elog(a,b,c,d)
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#define debug_elog5(a,b,c,d,e) elog(a,b,c,d,e)
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#define debug_elog6(a,b,c,d,e,f) elog(a,b,c,d,e,f)
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#else
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#define debug_elog2(a,b)
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#define debug_elog3(a,b,c)
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#define debug_elog4(a,b,c,d)
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#define debug_elog5(a,b,c,d,e)
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#define debug_elog6(a,b,c,d,e,f)
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#endif
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/* internal MultiXactId management */
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static void MultiXactIdSetOldestVisible(void);
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static void RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
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int nmembers, MultiXactMember *members);
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static MultiXactId GetNewMultiXactId(int nmembers, MultiXactOffset *offset);
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/* MultiXact cache management */
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static int mxactMemberComparator(const void *arg1, const void *arg2);
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static MultiXactId mXactCacheGetBySet(int nmembers, MultiXactMember *members);
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static int mXactCacheGetById(MultiXactId multi, MultiXactMember **members);
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static void mXactCachePut(MultiXactId multi, int nmembers,
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MultiXactMember *members);
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static char *mxstatus_to_string(MultiXactStatus status);
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/* management of SLRU infrastructure */
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static int ZeroMultiXactOffsetPage(int pageno, bool writeXlog);
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static int ZeroMultiXactMemberPage(int pageno, bool writeXlog);
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static bool MultiXactOffsetPagePrecedes(int page1, int page2);
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static bool MultiXactMemberPagePrecedes(int page1, int page2);
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static bool MultiXactOffsetPrecedes(MultiXactOffset offset1,
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MultiXactOffset offset2);
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static void ExtendMultiXactOffset(MultiXactId multi);
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static void ExtendMultiXactMember(MultiXactOffset offset, int nmembers);
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static bool MultiXactOffsetWouldWrap(MultiXactOffset boundary,
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MultiXactOffset start, uint32 distance);
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static bool SetOffsetVacuumLimit(bool is_startup);
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static bool find_multixact_start(MultiXactId multi, MultiXactOffset *result);
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static void WriteMZeroPageXlogRec(int pageno, uint8 info);
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static void WriteMTruncateXlogRec(Oid oldestMultiDB,
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MultiXactId startTruncOff,
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MultiXactId endTruncOff,
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MultiXactOffset startTruncMemb,
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MultiXactOffset endTruncMemb);
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/*
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* MultiXactIdCreate
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* Construct a MultiXactId representing two TransactionIds.
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*
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* The two XIDs must be different, or be requesting different statuses.
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*
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* NB - we don't worry about our local MultiXactId cache here, because that
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* is handled by the lower-level routines.
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*/
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MultiXactId
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MultiXactIdCreate(TransactionId xid1, MultiXactStatus status1,
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TransactionId xid2, MultiXactStatus status2)
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{
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MultiXactId newMulti;
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MultiXactMember members[2];
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AssertArg(TransactionIdIsValid(xid1));
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AssertArg(TransactionIdIsValid(xid2));
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Assert(!TransactionIdEquals(xid1, xid2) || (status1 != status2));
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/* MultiXactIdSetOldestMember() must have been called already. */
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Assert(MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]));
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/*
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* Note: unlike MultiXactIdExpand, we don't bother to check that both XIDs
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* are still running. In typical usage, xid2 will be our own XID and the
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* caller just did a check on xid1, so it'd be wasted effort.
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*/
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members[0].xid = xid1;
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members[0].status = status1;
|
|
members[1].xid = xid2;
|
|
members[1].status = status2;
|
|
|
|
newMulti = MultiXactIdCreateFromMembers(2, members);
|
|
|
|
debug_elog3(DEBUG2, "Create: %s",
|
|
mxid_to_string(newMulti, 2, members));
|
|
|
|
return newMulti;
|
|
}
|
|
|
|
/*
|
|
* MultiXactIdExpand
|
|
* Add a TransactionId to a pre-existing MultiXactId.
|
|
*
|
|
* If the TransactionId is already a member of the passed MultiXactId with the
|
|
* same status, just return it as-is.
|
|
*
|
|
* Note that we do NOT actually modify the membership of a pre-existing
|
|
* MultiXactId; instead we create a new one. This is necessary to avoid
|
|
* a race condition against code trying to wait for one MultiXactId to finish;
|
|
* see notes in heapam.c.
|
|
*
|
|
* NB - we don't worry about our local MultiXactId cache here, because that
|
|
* is handled by the lower-level routines.
|
|
*
|
|
* Note: It is critical that MultiXactIds that come from an old cluster (i.e.
|
|
* one upgraded by pg_upgrade from a cluster older than this feature) are not
|
|
* passed in.
|
|
*/
|
|
MultiXactId
|
|
MultiXactIdExpand(MultiXactId multi, TransactionId xid, MultiXactStatus status)
|
|
{
|
|
MultiXactId newMulti;
|
|
MultiXactMember *members;
|
|
MultiXactMember *newMembers;
|
|
int nmembers;
|
|
int i;
|
|
int j;
|
|
|
|
AssertArg(MultiXactIdIsValid(multi));
|
|
AssertArg(TransactionIdIsValid(xid));
|
|
|
|
/* MultiXactIdSetOldestMember() must have been called already. */
|
|
Assert(MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]));
|
|
|
|
debug_elog5(DEBUG2, "Expand: received multi %u, xid %u status %s",
|
|
multi, xid, mxstatus_to_string(status));
|
|
|
|
/*
|
|
* Note: we don't allow for old multis here. The reason is that the only
|
|
* caller of this function does a check that the multixact is no longer
|
|
* running.
|
|
*/
|
|
nmembers = GetMultiXactIdMembers(multi, &members, false, false);
|
|
|
|
if (nmembers < 0)
|
|
{
|
|
MultiXactMember member;
|
|
|
|
/*
|
|
* The MultiXactId is obsolete. This can only happen if all the
|
|
* MultiXactId members stop running between the caller checking and
|
|
* passing it to us. It would be better to return that fact to the
|
|
* caller, but it would complicate the API and it's unlikely to happen
|
|
* too often, so just deal with it by creating a singleton MultiXact.
|
|
*/
|
|
member.xid = xid;
|
|
member.status = status;
|
|
newMulti = MultiXactIdCreateFromMembers(1, &member);
|
|
|
|
debug_elog4(DEBUG2, "Expand: %u has no members, create singleton %u",
|
|
multi, newMulti);
|
|
return newMulti;
|
|
}
|
|
|
|
/*
|
|
* If the TransactionId is already a member of the MultiXactId with the
|
|
* same status, just return the existing MultiXactId.
|
|
*/
|
|
for (i = 0; i < nmembers; i++)
|
|
{
|
|
if (TransactionIdEquals(members[i].xid, xid) &&
|
|
(members[i].status == status))
|
|
{
|
|
debug_elog4(DEBUG2, "Expand: %u is already a member of %u",
|
|
xid, multi);
|
|
pfree(members);
|
|
return multi;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Determine which of the members of the MultiXactId are still of
|
|
* interest. This is any running transaction, and also any transaction
|
|
* that grabbed something stronger than just a lock and was committed. (An
|
|
* update that aborted is of no interest here; and having more than one
|
|
* update Xid in a multixact would cause errors elsewhere.)
|
|
*
|
|
* Removing dead members is not just an optimization: freezing of tuples
|
|
* whose Xmax are multis depends on this behavior.
|
|
*
|
|
* Note we have the same race condition here as above: j could be 0 at the
|
|
* end of the loop.
|
|
*/
|
|
newMembers = (MultiXactMember *)
|
|
palloc(sizeof(MultiXactMember) * (nmembers + 1));
|
|
|
|
for (i = 0, j = 0; i < nmembers; i++)
|
|
{
|
|
if (TransactionIdIsInProgress(members[i].xid) ||
|
|
(ISUPDATE_from_mxstatus(members[i].status) &&
|
|
TransactionIdDidCommit(members[i].xid)))
|
|
{
|
|
newMembers[j].xid = members[i].xid;
|
|
newMembers[j++].status = members[i].status;
|
|
}
|
|
}
|
|
|
|
newMembers[j].xid = xid;
|
|
newMembers[j++].status = status;
|
|
newMulti = MultiXactIdCreateFromMembers(j, newMembers);
|
|
|
|
pfree(members);
|
|
pfree(newMembers);
|
|
|
|
debug_elog3(DEBUG2, "Expand: returning new multi %u", newMulti);
|
|
|
|
return newMulti;
|
|
}
|
|
|
|
/*
|
|
* MultiXactIdIsRunning
|
|
* Returns whether a MultiXactId is "running".
|
|
*
|
|
* We return true if at least one member of the given MultiXactId is still
|
|
* running. Note that a "false" result is certain not to change,
|
|
* because it is not legal to add members to an existing MultiXactId.
|
|
*
|
|
* Caller is expected to have verified that the multixact does not come from
|
|
* a pg_upgraded share-locked tuple.
|
|
*/
|
|
bool
|
|
MultiXactIdIsRunning(MultiXactId multi, bool isLockOnly)
|
|
{
|
|
MultiXactMember *members;
|
|
int nmembers;
|
|
int i;
|
|
|
|
debug_elog3(DEBUG2, "IsRunning %u?", multi);
|
|
|
|
/*
|
|
* "false" here means we assume our callers have checked that the given
|
|
* multi cannot possibly come from a pg_upgraded database.
|
|
*/
|
|
nmembers = GetMultiXactIdMembers(multi, &members, false, isLockOnly);
|
|
|
|
if (nmembers <= 0)
|
|
{
|
|
debug_elog2(DEBUG2, "IsRunning: no members");
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Checking for myself is cheap compared to looking in shared memory;
|
|
* return true if any live subtransaction of the current top-level
|
|
* transaction is a member.
|
|
*
|
|
* This is not needed for correctness, it's just a fast path.
|
|
*/
|
|
for (i = 0; i < nmembers; i++)
|
|
{
|
|
if (TransactionIdIsCurrentTransactionId(members[i].xid))
|
|
{
|
|
debug_elog3(DEBUG2, "IsRunning: I (%d) am running!", i);
|
|
pfree(members);
|
|
return true;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* This could be made faster by having another entry point in procarray.c,
|
|
* walking the PGPROC array only once for all the members. But in most
|
|
* cases nmembers should be small enough that it doesn't much matter.
|
|
*/
|
|
for (i = 0; i < nmembers; i++)
|
|
{
|
|
if (TransactionIdIsInProgress(members[i].xid))
|
|
{
|
|
debug_elog4(DEBUG2, "IsRunning: member %d (%u) is running",
|
|
i, members[i].xid);
|
|
pfree(members);
|
|
return true;
|
|
}
|
|
}
|
|
|
|
pfree(members);
|
|
|
|
debug_elog3(DEBUG2, "IsRunning: %u is not running", multi);
|
|
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* MultiXactIdSetOldestMember
|
|
* Save the oldest MultiXactId this transaction could be a member of.
|
|
*
|
|
* We set the OldestMemberMXactId for a given transaction the first time it's
|
|
* going to do some operation that might require a MultiXactId (tuple lock,
|
|
* update or delete). We need to do this even if we end up using a
|
|
* TransactionId instead of a MultiXactId, because there is a chance that
|
|
* another transaction would add our XID to a MultiXactId.
|
|
*
|
|
* The value to set is the next-to-be-assigned MultiXactId, so this is meant to
|
|
* be called just before doing any such possibly-MultiXactId-able operation.
|
|
*/
|
|
void
|
|
MultiXactIdSetOldestMember(void)
|
|
{
|
|
if (!MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]))
|
|
{
|
|
MultiXactId nextMXact;
|
|
|
|
/*
|
|
* You might think we don't need to acquire a lock here, since
|
|
* fetching and storing of TransactionIds is probably atomic, but in
|
|
* fact we do: suppose we pick up nextMXact and then lose the CPU for
|
|
* a long time. Someone else could advance nextMXact, and then
|
|
* another someone else could compute an OldestVisibleMXactId that
|
|
* would be after the value we are going to store when we get control
|
|
* back. Which would be wrong.
|
|
*
|
|
* Note that a shared lock is sufficient, because it's enough to stop
|
|
* someone from advancing nextMXact; and nobody else could be trying
|
|
* to write to our OldestMember entry, only reading (and we assume
|
|
* storing it is atomic.)
|
|
*/
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
|
|
/*
|
|
* We have to beware of the possibility that nextMXact is in the
|
|
* wrapped-around state. We don't fix the counter itself here, but we
|
|
* must be sure to store a valid value in our array entry.
|
|
*/
|
|
nextMXact = MultiXactState->nextMXact;
|
|
if (nextMXact < FirstMultiXactId)
|
|
nextMXact = FirstMultiXactId;
|
|
|
|
OldestMemberMXactId[MyBackendId] = nextMXact;
|
|
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
debug_elog4(DEBUG2, "MultiXact: setting OldestMember[%d] = %u",
|
|
MyBackendId, nextMXact);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* MultiXactIdSetOldestVisible
|
|
* Save the oldest MultiXactId this transaction considers possibly live.
|
|
*
|
|
* We set the OldestVisibleMXactId for a given transaction the first time
|
|
* it's going to inspect any MultiXactId. Once we have set this, we are
|
|
* guaranteed that the checkpointer won't truncate off SLRU data for
|
|
* MultiXactIds at or after our OldestVisibleMXactId.
|
|
*
|
|
* The value to set is the oldest of nextMXact and all the valid per-backend
|
|
* OldestMemberMXactId[] entries. Because of the locking we do, we can be
|
|
* certain that no subsequent call to MultiXactIdSetOldestMember can set
|
|
* an OldestMemberMXactId[] entry older than what we compute here. Therefore
|
|
* there is no live transaction, now or later, that can be a member of any
|
|
* MultiXactId older than the OldestVisibleMXactId we compute here.
|
|
*/
|
|
static void
|
|
MultiXactIdSetOldestVisible(void)
|
|
{
|
|
if (!MultiXactIdIsValid(OldestVisibleMXactId[MyBackendId]))
|
|
{
|
|
MultiXactId oldestMXact;
|
|
int i;
|
|
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* We have to beware of the possibility that nextMXact is in the
|
|
* wrapped-around state. We don't fix the counter itself here, but we
|
|
* must be sure to store a valid value in our array entry.
|
|
*/
|
|
oldestMXact = MultiXactState->nextMXact;
|
|
if (oldestMXact < FirstMultiXactId)
|
|
oldestMXact = FirstMultiXactId;
|
|
|
|
for (i = 1; i <= MaxOldestSlot; i++)
|
|
{
|
|
MultiXactId thisoldest = OldestMemberMXactId[i];
|
|
|
|
if (MultiXactIdIsValid(thisoldest) &&
|
|
MultiXactIdPrecedes(thisoldest, oldestMXact))
|
|
oldestMXact = thisoldest;
|
|
}
|
|
|
|
OldestVisibleMXactId[MyBackendId] = oldestMXact;
|
|
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
debug_elog4(DEBUG2, "MultiXact: setting OldestVisible[%d] = %u",
|
|
MyBackendId, oldestMXact);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* ReadNextMultiXactId
|
|
* Return the next MultiXactId to be assigned, but don't allocate it
|
|
*/
|
|
MultiXactId
|
|
ReadNextMultiXactId(void)
|
|
{
|
|
MultiXactId mxid;
|
|
|
|
/* XXX we could presumably do this without a lock. */
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
mxid = MultiXactState->nextMXact;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
if (mxid < FirstMultiXactId)
|
|
mxid = FirstMultiXactId;
|
|
|
|
return mxid;
|
|
}
|
|
|
|
/*
|
|
* ReadMultiXactIdRange
|
|
* Get the range of IDs that may still be referenced by a relation.
|
|
*/
|
|
void
|
|
ReadMultiXactIdRange(MultiXactId *oldest, MultiXactId *next)
|
|
{
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
*oldest = MultiXactState->oldestMultiXactId;
|
|
*next = MultiXactState->nextMXact;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
if (*oldest < FirstMultiXactId)
|
|
*oldest = FirstMultiXactId;
|
|
if (*next < FirstMultiXactId)
|
|
*next = FirstMultiXactId;
|
|
}
|
|
|
|
|
|
/*
|
|
* MultiXactIdCreateFromMembers
|
|
* Make a new MultiXactId from the specified set of members
|
|
*
|
|
* Make XLOG, SLRU and cache entries for a new MultiXactId, recording the
|
|
* given TransactionIds as members. Returns the newly created MultiXactId.
|
|
*
|
|
* NB: the passed members[] array will be sorted in-place.
|
|
*/
|
|
MultiXactId
|
|
MultiXactIdCreateFromMembers(int nmembers, MultiXactMember *members)
|
|
{
|
|
MultiXactId multi;
|
|
MultiXactOffset offset;
|
|
xl_multixact_create xlrec;
|
|
|
|
debug_elog3(DEBUG2, "Create: %s",
|
|
mxid_to_string(InvalidMultiXactId, nmembers, members));
|
|
|
|
/*
|
|
* See if the same set of members already exists in our cache; if so, just
|
|
* re-use that MultiXactId. (Note: it might seem that looking in our
|
|
* cache is insufficient, and we ought to search disk to see if a
|
|
* duplicate definition already exists. But since we only ever create
|
|
* MultiXacts containing our own XID, in most cases any such MultiXacts
|
|
* were in fact created by us, and so will be in our cache. There are
|
|
* corner cases where someone else added us to a MultiXact without our
|
|
* knowledge, but it's not worth checking for.)
|
|
*/
|
|
multi = mXactCacheGetBySet(nmembers, members);
|
|
if (MultiXactIdIsValid(multi))
|
|
{
|
|
debug_elog2(DEBUG2, "Create: in cache!");
|
|
return multi;
|
|
}
|
|
|
|
/* Verify that there is a single update Xid among the given members. */
|
|
{
|
|
int i;
|
|
bool has_update = false;
|
|
|
|
for (i = 0; i < nmembers; i++)
|
|
{
|
|
if (ISUPDATE_from_mxstatus(members[i].status))
|
|
{
|
|
if (has_update)
|
|
elog(ERROR, "new multixact has more than one updating member");
|
|
has_update = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Assign the MXID and offsets range to use, and make sure there is space
|
|
* in the OFFSETs and MEMBERs files. NB: this routine does
|
|
* START_CRIT_SECTION().
|
|
*
|
|
* Note: unlike MultiXactIdCreate and MultiXactIdExpand, we do not check
|
|
* that we've called MultiXactIdSetOldestMember here. This is because
|
|
* this routine is used in some places to create new MultiXactIds of which
|
|
* the current backend is not a member, notably during freezing of multis
|
|
* in vacuum. During vacuum, in particular, it would be unacceptable to
|
|
* keep OldestMulti set, in case it runs for long.
|
|
*/
|
|
multi = GetNewMultiXactId(nmembers, &offset);
|
|
|
|
/* Make an XLOG entry describing the new MXID. */
|
|
xlrec.mid = multi;
|
|
xlrec.moff = offset;
|
|
xlrec.nmembers = nmembers;
|
|
|
|
/*
|
|
* XXX Note: there's a lot of padding space in MultiXactMember. We could
|
|
* find a more compact representation of this Xlog record -- perhaps all
|
|
* the status flags in one XLogRecData, then all the xids in another one?
|
|
* Not clear that it's worth the trouble though.
|
|
*/
|
|
XLogBeginInsert();
|
|
XLogRegisterData((char *) (&xlrec), SizeOfMultiXactCreate);
|
|
XLogRegisterData((char *) members, nmembers * sizeof(MultiXactMember));
|
|
|
|
(void) XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_CREATE_ID);
|
|
|
|
/* Now enter the information into the OFFSETs and MEMBERs logs */
|
|
RecordNewMultiXact(multi, offset, nmembers, members);
|
|
|
|
/* Done with critical section */
|
|
END_CRIT_SECTION();
|
|
|
|
/* Store the new MultiXactId in the local cache, too */
|
|
mXactCachePut(multi, nmembers, members);
|
|
|
|
debug_elog2(DEBUG2, "Create: all done");
|
|
|
|
return multi;
|
|
}
|
|
|
|
/*
|
|
* RecordNewMultiXact
|
|
* Write info about a new multixact into the offsets and members files
|
|
*
|
|
* This is broken out of MultiXactIdCreateFromMembers so that xlog replay can
|
|
* use it.
|
|
*/
|
|
static void
|
|
RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
|
|
int nmembers, MultiXactMember *members)
|
|
{
|
|
int pageno;
|
|
int prev_pageno;
|
|
int entryno;
|
|
int slotno;
|
|
MultiXactOffset *offptr;
|
|
int i;
|
|
|
|
LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
|
|
|
|
pageno = MultiXactIdToOffsetPage(multi);
|
|
entryno = MultiXactIdToOffsetEntry(multi);
|
|
|
|
/*
|
|
* Note: we pass the MultiXactId to SimpleLruReadPage as the "transaction"
|
|
* to complain about if there's any I/O error. This is kinda bogus, but
|
|
* since the errors will always give the full pathname, it should be clear
|
|
* enough that a MultiXactId is really involved. Perhaps someday we'll
|
|
* take the trouble to generalize the slru.c error reporting code.
|
|
*/
|
|
slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
|
|
offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
|
|
offptr += entryno;
|
|
|
|
*offptr = offset;
|
|
|
|
MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
|
|
|
|
/* Exchange our lock */
|
|
LWLockRelease(MultiXactOffsetSLRULock);
|
|
|
|
LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
|
|
|
|
prev_pageno = -1;
|
|
|
|
for (i = 0; i < nmembers; i++, offset++)
|
|
{
|
|
TransactionId *memberptr;
|
|
uint32 *flagsptr;
|
|
uint32 flagsval;
|
|
int bshift;
|
|
int flagsoff;
|
|
int memberoff;
|
|
|
|
Assert(members[i].status <= MultiXactStatusUpdate);
|
|
|
|
pageno = MXOffsetToMemberPage(offset);
|
|
memberoff = MXOffsetToMemberOffset(offset);
|
|
flagsoff = MXOffsetToFlagsOffset(offset);
|
|
bshift = MXOffsetToFlagsBitShift(offset);
|
|
|
|
if (pageno != prev_pageno)
|
|
{
|
|
slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
|
|
prev_pageno = pageno;
|
|
}
|
|
|
|
memberptr = (TransactionId *)
|
|
(MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
|
|
|
|
*memberptr = members[i].xid;
|
|
|
|
flagsptr = (uint32 *)
|
|
(MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
|
|
|
|
flagsval = *flagsptr;
|
|
flagsval &= ~(((1 << MXACT_MEMBER_BITS_PER_XACT) - 1) << bshift);
|
|
flagsval |= (members[i].status << bshift);
|
|
*flagsptr = flagsval;
|
|
|
|
MultiXactMemberCtl->shared->page_dirty[slotno] = true;
|
|
}
|
|
|
|
LWLockRelease(MultiXactMemberSLRULock);
|
|
}
|
|
|
|
/*
|
|
* GetNewMultiXactId
|
|
* Get the next MultiXactId.
|
|
*
|
|
* Also, reserve the needed amount of space in the "members" area. The
|
|
* starting offset of the reserved space is returned in *offset.
|
|
*
|
|
* This may generate XLOG records for expansion of the offsets and/or members
|
|
* files. Unfortunately, we have to do that while holding MultiXactGenLock
|
|
* to avoid race conditions --- the XLOG record for zeroing a page must appear
|
|
* before any backend can possibly try to store data in that page!
|
|
*
|
|
* We start a critical section before advancing the shared counters. The
|
|
* caller must end the critical section after writing SLRU data.
|
|
*/
|
|
static MultiXactId
|
|
GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
|
|
{
|
|
MultiXactId result;
|
|
MultiXactOffset nextOffset;
|
|
|
|
debug_elog3(DEBUG2, "GetNew: for %d xids", nmembers);
|
|
|
|
/* safety check, we should never get this far in a HS standby */
|
|
if (RecoveryInProgress())
|
|
elog(ERROR, "cannot assign MultiXactIds during recovery");
|
|
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
|
|
/* Handle wraparound of the nextMXact counter */
|
|
if (MultiXactState->nextMXact < FirstMultiXactId)
|
|
MultiXactState->nextMXact = FirstMultiXactId;
|
|
|
|
/* Assign the MXID */
|
|
result = MultiXactState->nextMXact;
|
|
|
|
/*----------
|
|
* Check to see if it's safe to assign another MultiXactId. This protects
|
|
* against catastrophic data loss due to multixact wraparound. The basic
|
|
* rules are:
|
|
*
|
|
* If we're past multiVacLimit or the safe threshold for member storage
|
|
* space, or we don't know what the safe threshold for member storage is,
|
|
* start trying to force autovacuum cycles.
|
|
* If we're past multiWarnLimit, start issuing warnings.
|
|
* If we're past multiStopLimit, refuse to create new MultiXactIds.
|
|
*
|
|
* Note these are pretty much the same protections in GetNewTransactionId.
|
|
*----------
|
|
*/
|
|
if (!MultiXactIdPrecedes(result, MultiXactState->multiVacLimit))
|
|
{
|
|
/*
|
|
* For safety's sake, we release MultiXactGenLock while sending
|
|
* signals, warnings, etc. This is not so much because we care about
|
|
* preserving concurrency in this situation, as to avoid any
|
|
* possibility of deadlock while doing get_database_name(). First,
|
|
* copy all the shared values we'll need in this path.
|
|
*/
|
|
MultiXactId multiWarnLimit = MultiXactState->multiWarnLimit;
|
|
MultiXactId multiStopLimit = MultiXactState->multiStopLimit;
|
|
MultiXactId multiWrapLimit = MultiXactState->multiWrapLimit;
|
|
Oid oldest_datoid = MultiXactState->oldestMultiXactDB;
|
|
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
if (IsUnderPostmaster &&
|
|
!MultiXactIdPrecedes(result, multiStopLimit))
|
|
{
|
|
char *oldest_datname = get_database_name(oldest_datoid);
|
|
|
|
/*
|
|
* Immediately kick autovacuum into action as we're already in
|
|
* ERROR territory.
|
|
*/
|
|
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
|
|
|
|
/* complain even if that DB has disappeared */
|
|
if (oldest_datname)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
|
|
errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database \"%s\"",
|
|
oldest_datname),
|
|
errhint("Execute a database-wide VACUUM in that database.\n"
|
|
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
|
|
else
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
|
|
errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database with OID %u",
|
|
oldest_datoid),
|
|
errhint("Execute a database-wide VACUUM in that database.\n"
|
|
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
|
|
}
|
|
|
|
/*
|
|
* To avoid swamping the postmaster with signals, we issue the autovac
|
|
* request only once per 64K multis generated. This still gives
|
|
* plenty of chances before we get into real trouble.
|
|
*/
|
|
if (IsUnderPostmaster && (result % 65536) == 0)
|
|
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
|
|
|
|
if (!MultiXactIdPrecedes(result, multiWarnLimit))
|
|
{
|
|
char *oldest_datname = get_database_name(oldest_datoid);
|
|
|
|
/* complain even if that DB has disappeared */
|
|
if (oldest_datname)
|
|
ereport(WARNING,
|
|
(errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
|
|
"database \"%s\" must be vacuumed before %u more MultiXactIds are used",
|
|
multiWrapLimit - result,
|
|
oldest_datname,
|
|
multiWrapLimit - result),
|
|
errhint("Execute a database-wide VACUUM in that database.\n"
|
|
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
|
|
else
|
|
ereport(WARNING,
|
|
(errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
|
|
"database with OID %u must be vacuumed before %u more MultiXactIds are used",
|
|
multiWrapLimit - result,
|
|
oldest_datoid,
|
|
multiWrapLimit - result),
|
|
errhint("Execute a database-wide VACUUM in that database.\n"
|
|
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
|
|
}
|
|
|
|
/* Re-acquire lock and start over */
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
result = MultiXactState->nextMXact;
|
|
if (result < FirstMultiXactId)
|
|
result = FirstMultiXactId;
|
|
}
|
|
|
|
/* Make sure there is room for the MXID in the file. */
|
|
ExtendMultiXactOffset(result);
|
|
|
|
/*
|
|
* Reserve the members space, similarly to above. Also, be careful not to
|
|
* return zero as the starting offset for any multixact. See
|
|
* GetMultiXactIdMembers() for motivation.
|
|
*/
|
|
nextOffset = MultiXactState->nextOffset;
|
|
if (nextOffset == 0)
|
|
{
|
|
*offset = 1;
|
|
nmembers++; /* allocate member slot 0 too */
|
|
}
|
|
else
|
|
*offset = nextOffset;
|
|
|
|
/*----------
|
|
* Protect against overrun of the members space as well, with the
|
|
* following rules:
|
|
*
|
|
* If we're past offsetStopLimit, refuse to generate more multis.
|
|
* If we're close to offsetStopLimit, emit a warning.
|
|
*
|
|
* Arbitrarily, we start emitting warnings when we're 20 segments or less
|
|
* from offsetStopLimit.
|
|
*
|
|
* Note we haven't updated the shared state yet, so if we fail at this
|
|
* point, the multixact ID we grabbed can still be used by the next guy.
|
|
*
|
|
* Note that there is no point in forcing autovacuum runs here: the
|
|
* multixact freeze settings would have to be reduced for that to have any
|
|
* effect.
|
|
*----------
|
|
*/
|
|
#define OFFSET_WARN_SEGMENTS 20
|
|
if (MultiXactState->oldestOffsetKnown &&
|
|
MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit, nextOffset,
|
|
nmembers))
|
|
{
|
|
/* see comment in the corresponding offsets wraparound case */
|
|
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
|
|
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
|
|
errmsg("multixact \"members\" limit exceeded"),
|
|
errdetail_plural("This command would create a multixact with %u members, but the remaining space is only enough for %u member.",
|
|
"This command would create a multixact with %u members, but the remaining space is only enough for %u members.",
|
|
MultiXactState->offsetStopLimit - nextOffset - 1,
|
|
nmembers,
|
|
MultiXactState->offsetStopLimit - nextOffset - 1),
|
|
errhint("Execute a database-wide VACUUM in database with OID %u with reduced vacuum_multixact_freeze_min_age and vacuum_multixact_freeze_table_age settings.",
|
|
MultiXactState->oldestMultiXactDB)));
|
|
}
|
|
|
|
/*
|
|
* Check whether we should kick autovacuum into action, to prevent members
|
|
* wraparound. NB we use a much larger window to trigger autovacuum than
|
|
* just the warning limit. The warning is just a measure of last resort -
|
|
* this is in line with GetNewTransactionId's behaviour.
|
|
*/
|
|
if (!MultiXactState->oldestOffsetKnown ||
|
|
(MultiXactState->nextOffset - MultiXactState->oldestOffset
|
|
> MULTIXACT_MEMBER_SAFE_THRESHOLD))
|
|
{
|
|
/*
|
|
* To avoid swamping the postmaster with signals, we issue the autovac
|
|
* request only when crossing a segment boundary. With default
|
|
* compilation settings that's roughly after 50k members. This still
|
|
* gives plenty of chances before we get into real trouble.
|
|
*/
|
|
if ((MXOffsetToMemberPage(nextOffset) / SLRU_PAGES_PER_SEGMENT) !=
|
|
(MXOffsetToMemberPage(nextOffset + nmembers) / SLRU_PAGES_PER_SEGMENT))
|
|
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
|
|
}
|
|
|
|
if (MultiXactState->oldestOffsetKnown &&
|
|
MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit,
|
|
nextOffset,
|
|
nmembers + MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT * OFFSET_WARN_SEGMENTS))
|
|
ereport(WARNING,
|
|
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
|
|
errmsg_plural("database with OID %u must be vacuumed before %d more multixact member is used",
|
|
"database with OID %u must be vacuumed before %d more multixact members are used",
|
|
MultiXactState->offsetStopLimit - nextOffset + nmembers,
|
|
MultiXactState->oldestMultiXactDB,
|
|
MultiXactState->offsetStopLimit - nextOffset + nmembers),
|
|
errhint("Execute a database-wide VACUUM in that database with reduced vacuum_multixact_freeze_min_age and vacuum_multixact_freeze_table_age settings.")));
|
|
|
|
ExtendMultiXactMember(nextOffset, nmembers);
|
|
|
|
/*
|
|
* Critical section from here until caller has written the data into the
|
|
* just-reserved SLRU space; we don't want to error out with a partly
|
|
* written MultiXact structure. (In particular, failing to write our
|
|
* start offset after advancing nextMXact would effectively corrupt the
|
|
* previous MultiXact.)
|
|
*/
|
|
START_CRIT_SECTION();
|
|
|
|
/*
|
|
* Advance counters. As in GetNewTransactionId(), this must not happen
|
|
* until after file extension has succeeded!
|
|
*
|
|
* We don't care about MultiXactId wraparound here; it will be handled by
|
|
* the next iteration. But note that nextMXact may be InvalidMultiXactId
|
|
* or the first value on a segment-beginning page after this routine
|
|
* exits, so anyone else looking at the variable must be prepared to deal
|
|
* with either case. Similarly, nextOffset may be zero, but we won't use
|
|
* that as the actual start offset of the next multixact.
|
|
*/
|
|
(MultiXactState->nextMXact)++;
|
|
|
|
MultiXactState->nextOffset += nmembers;
|
|
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
debug_elog4(DEBUG2, "GetNew: returning %u offset %u", result, *offset);
|
|
return result;
|
|
}
|
|
|
|
/*
|
|
* GetMultiXactIdMembers
|
|
* Return the set of MultiXactMembers that make up a MultiXactId
|
|
*
|
|
* Return value is the number of members found, or -1 if there are none,
|
|
* and *members is set to a newly palloc'ed array of members. It's the
|
|
* caller's responsibility to free it when done with it.
|
|
*
|
|
* from_pgupgrade must be passed as true if and only if only the multixact
|
|
* corresponds to a value from a tuple that was locked in a 9.2-or-older
|
|
* installation and later pg_upgrade'd (that is, the infomask is
|
|
* HEAP_LOCKED_UPGRADED). In this case, we know for certain that no members
|
|
* can still be running, so we return -1 just like for an empty multixact
|
|
* without any further checking. It would be wrong to try to resolve such a
|
|
* multixact: either the multixact is within the current valid multixact
|
|
* range, in which case the returned result would be bogus, or outside that
|
|
* range, in which case an error would be raised.
|
|
*
|
|
* In all other cases, the passed multixact must be within the known valid
|
|
* range, that is, greater to or equal than oldestMultiXactId, and less than
|
|
* nextMXact. Otherwise, an error is raised.
|
|
*
|
|
* onlyLock must be set to true if caller is certain that the given multi
|
|
* is used only to lock tuples; can be false without loss of correctness,
|
|
* but passing a true means we can return quickly without checking for
|
|
* old updates.
|
|
*/
|
|
int
|
|
GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members,
|
|
bool from_pgupgrade, bool onlyLock)
|
|
{
|
|
int pageno;
|
|
int prev_pageno;
|
|
int entryno;
|
|
int slotno;
|
|
MultiXactOffset *offptr;
|
|
MultiXactOffset offset;
|
|
int length;
|
|
int truelength;
|
|
int i;
|
|
MultiXactId oldestMXact;
|
|
MultiXactId nextMXact;
|
|
MultiXactId tmpMXact;
|
|
MultiXactOffset nextOffset;
|
|
MultiXactMember *ptr;
|
|
|
|
debug_elog3(DEBUG2, "GetMembers: asked for %u", multi);
|
|
|
|
if (!MultiXactIdIsValid(multi) || from_pgupgrade)
|
|
return -1;
|
|
|
|
/* See if the MultiXactId is in the local cache */
|
|
length = mXactCacheGetById(multi, members);
|
|
if (length >= 0)
|
|
{
|
|
debug_elog3(DEBUG2, "GetMembers: found %s in the cache",
|
|
mxid_to_string(multi, length, *members));
|
|
return length;
|
|
}
|
|
|
|
/* Set our OldestVisibleMXactId[] entry if we didn't already */
|
|
MultiXactIdSetOldestVisible();
|
|
|
|
/*
|
|
* If we know the multi is used only for locking and not for updates, then
|
|
* we can skip checking if the value is older than our oldest visible
|
|
* multi. It cannot possibly still be running.
|
|
*/
|
|
if (onlyLock &&
|
|
MultiXactIdPrecedes(multi, OldestVisibleMXactId[MyBackendId]))
|
|
{
|
|
debug_elog2(DEBUG2, "GetMembers: a locker-only multi is too old");
|
|
*members = NULL;
|
|
return -1;
|
|
}
|
|
|
|
/*
|
|
* We check known limits on MultiXact before resorting to the SLRU area.
|
|
*
|
|
* An ID older than MultiXactState->oldestMultiXactId cannot possibly be
|
|
* useful; it has already been removed, or will be removed shortly, by
|
|
* truncation. If one is passed, an error is raised.
|
|
*
|
|
* Also, an ID >= nextMXact shouldn't ever be seen here; if it is seen, it
|
|
* implies undetected ID wraparound has occurred. This raises a hard
|
|
* error.
|
|
*
|
|
* Shared lock is enough here since we aren't modifying any global state.
|
|
* Acquire it just long enough to grab the current counter values. We may
|
|
* need both nextMXact and nextOffset; see below.
|
|
*/
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
|
|
oldestMXact = MultiXactState->oldestMultiXactId;
|
|
nextMXact = MultiXactState->nextMXact;
|
|
nextOffset = MultiXactState->nextOffset;
|
|
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
if (MultiXactIdPrecedes(multi, oldestMXact))
|
|
{
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_INTERNAL_ERROR),
|
|
errmsg("MultiXactId %u does no longer exist -- apparent wraparound",
|
|
multi)));
|
|
return -1;
|
|
}
|
|
|
|
if (!MultiXactIdPrecedes(multi, nextMXact))
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_INTERNAL_ERROR),
|
|
errmsg("MultiXactId %u has not been created yet -- apparent wraparound",
|
|
multi)));
|
|
|
|
/*
|
|
* Find out the offset at which we need to start reading MultiXactMembers
|
|
* and the number of members in the multixact. We determine the latter as
|
|
* the difference between this multixact's starting offset and the next
|
|
* one's. However, there are some corner cases to worry about:
|
|
*
|
|
* 1. This multixact may be the latest one created, in which case there is
|
|
* no next one to look at. In this case the nextOffset value we just
|
|
* saved is the correct endpoint.
|
|
*
|
|
* 2. The next multixact may still be in process of being filled in: that
|
|
* is, another process may have done GetNewMultiXactId but not yet written
|
|
* the offset entry for that ID. In that scenario, it is guaranteed that
|
|
* the offset entry for that multixact exists (because GetNewMultiXactId
|
|
* won't release MultiXactGenLock until it does) but contains zero
|
|
* (because we are careful to pre-zero offset pages). Because
|
|
* GetNewMultiXactId will never return zero as the starting offset for a
|
|
* multixact, when we read zero as the next multixact's offset, we know we
|
|
* have this case. We sleep for a bit and try again.
|
|
*
|
|
* 3. Because GetNewMultiXactId increments offset zero to offset one to
|
|
* handle case #2, there is an ambiguity near the point of offset
|
|
* wraparound. If we see next multixact's offset is one, is that our
|
|
* multixact's actual endpoint, or did it end at zero with a subsequent
|
|
* increment? We handle this using the knowledge that if the zero'th
|
|
* member slot wasn't filled, it'll contain zero, and zero isn't a valid
|
|
* transaction ID so it can't be a multixact member. Therefore, if we
|
|
* read a zero from the members array, just ignore it.
|
|
*
|
|
* This is all pretty messy, but the mess occurs only in infrequent corner
|
|
* cases, so it seems better than holding the MultiXactGenLock for a long
|
|
* time on every multixact creation.
|
|
*/
|
|
retry:
|
|
LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
|
|
|
|
pageno = MultiXactIdToOffsetPage(multi);
|
|
entryno = MultiXactIdToOffsetEntry(multi);
|
|
|
|
slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
|
|
offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
|
|
offptr += entryno;
|
|
offset = *offptr;
|
|
|
|
Assert(offset != 0);
|
|
|
|
/*
|
|
* Use the same increment rule as GetNewMultiXactId(), that is, don't
|
|
* handle wraparound explicitly until needed.
|
|
*/
|
|
tmpMXact = multi + 1;
|
|
|
|
if (nextMXact == tmpMXact)
|
|
{
|
|
/* Corner case 1: there is no next multixact */
|
|
length = nextOffset - offset;
|
|
}
|
|
else
|
|
{
|
|
MultiXactOffset nextMXOffset;
|
|
|
|
/* handle wraparound if needed */
|
|
if (tmpMXact < FirstMultiXactId)
|
|
tmpMXact = FirstMultiXactId;
|
|
|
|
prev_pageno = pageno;
|
|
|
|
pageno = MultiXactIdToOffsetPage(tmpMXact);
|
|
entryno = MultiXactIdToOffsetEntry(tmpMXact);
|
|
|
|
if (pageno != prev_pageno)
|
|
slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, tmpMXact);
|
|
|
|
offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
|
|
offptr += entryno;
|
|
nextMXOffset = *offptr;
|
|
|
|
if (nextMXOffset == 0)
|
|
{
|
|
/* Corner case 2: next multixact is still being filled in */
|
|
LWLockRelease(MultiXactOffsetSLRULock);
|
|
CHECK_FOR_INTERRUPTS();
|
|
pg_usleep(1000L);
|
|
goto retry;
|
|
}
|
|
|
|
length = nextMXOffset - offset;
|
|
}
|
|
|
|
LWLockRelease(MultiXactOffsetSLRULock);
|
|
|
|
ptr = (MultiXactMember *) palloc(length * sizeof(MultiXactMember));
|
|
*members = ptr;
|
|
|
|
/* Now get the members themselves. */
|
|
LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
|
|
|
|
truelength = 0;
|
|
prev_pageno = -1;
|
|
for (i = 0; i < length; i++, offset++)
|
|
{
|
|
TransactionId *xactptr;
|
|
uint32 *flagsptr;
|
|
int flagsoff;
|
|
int bshift;
|
|
int memberoff;
|
|
|
|
pageno = MXOffsetToMemberPage(offset);
|
|
memberoff = MXOffsetToMemberOffset(offset);
|
|
|
|
if (pageno != prev_pageno)
|
|
{
|
|
slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
|
|
prev_pageno = pageno;
|
|
}
|
|
|
|
xactptr = (TransactionId *)
|
|
(MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
|
|
|
|
if (!TransactionIdIsValid(*xactptr))
|
|
{
|
|
/* Corner case 3: we must be looking at unused slot zero */
|
|
Assert(offset == 0);
|
|
continue;
|
|
}
|
|
|
|
flagsoff = MXOffsetToFlagsOffset(offset);
|
|
bshift = MXOffsetToFlagsBitShift(offset);
|
|
flagsptr = (uint32 *) (MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
|
|
|
|
ptr[truelength].xid = *xactptr;
|
|
ptr[truelength].status = (*flagsptr >> bshift) & MXACT_MEMBER_XACT_BITMASK;
|
|
truelength++;
|
|
}
|
|
|
|
LWLockRelease(MultiXactMemberSLRULock);
|
|
|
|
/*
|
|
* Copy the result into the local cache.
|
|
*/
|
|
mXactCachePut(multi, truelength, ptr);
|
|
|
|
debug_elog3(DEBUG2, "GetMembers: no cache for %s",
|
|
mxid_to_string(multi, truelength, ptr));
|
|
return truelength;
|
|
}
|
|
|
|
/*
|
|
* mxactMemberComparator
|
|
* qsort comparison function for MultiXactMember
|
|
*
|
|
* We can't use wraparound comparison for XIDs because that does not respect
|
|
* the triangle inequality! Any old sort order will do.
|
|
*/
|
|
static int
|
|
mxactMemberComparator(const void *arg1, const void *arg2)
|
|
{
|
|
MultiXactMember member1 = *(const MultiXactMember *) arg1;
|
|
MultiXactMember member2 = *(const MultiXactMember *) arg2;
|
|
|
|
if (member1.xid > member2.xid)
|
|
return 1;
|
|
if (member1.xid < member2.xid)
|
|
return -1;
|
|
if (member1.status > member2.status)
|
|
return 1;
|
|
if (member1.status < member2.status)
|
|
return -1;
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* mXactCacheGetBySet
|
|
* returns a MultiXactId from the cache based on the set of
|
|
* TransactionIds that compose it, or InvalidMultiXactId if
|
|
* none matches.
|
|
*
|
|
* This is helpful, for example, if two transactions want to lock a huge
|
|
* table. By using the cache, the second will use the same MultiXactId
|
|
* for the majority of tuples, thus keeping MultiXactId usage low (saving
|
|
* both I/O and wraparound issues).
|
|
*
|
|
* NB: the passed members array will be sorted in-place.
|
|
*/
|
|
static MultiXactId
|
|
mXactCacheGetBySet(int nmembers, MultiXactMember *members)
|
|
{
|
|
dlist_iter iter;
|
|
|
|
debug_elog3(DEBUG2, "CacheGet: looking for %s",
|
|
mxid_to_string(InvalidMultiXactId, nmembers, members));
|
|
|
|
/* sort the array so comparison is easy */
|
|
qsort(members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
|
|
|
|
dlist_foreach(iter, &MXactCache)
|
|
{
|
|
mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
|
|
|
|
if (entry->nmembers != nmembers)
|
|
continue;
|
|
|
|
/*
|
|
* We assume the cache entries are sorted, and that the unused bits in
|
|
* "status" are zeroed.
|
|
*/
|
|
if (memcmp(members, entry->members, nmembers * sizeof(MultiXactMember)) == 0)
|
|
{
|
|
debug_elog3(DEBUG2, "CacheGet: found %u", entry->multi);
|
|
dlist_move_head(&MXactCache, iter.cur);
|
|
return entry->multi;
|
|
}
|
|
}
|
|
|
|
debug_elog2(DEBUG2, "CacheGet: not found :-(");
|
|
return InvalidMultiXactId;
|
|
}
|
|
|
|
/*
|
|
* mXactCacheGetById
|
|
* returns the composing MultiXactMember set from the cache for a
|
|
* given MultiXactId, if present.
|
|
*
|
|
* If successful, *xids is set to the address of a palloc'd copy of the
|
|
* MultiXactMember set. Return value is number of members, or -1 on failure.
|
|
*/
|
|
static int
|
|
mXactCacheGetById(MultiXactId multi, MultiXactMember **members)
|
|
{
|
|
dlist_iter iter;
|
|
|
|
debug_elog3(DEBUG2, "CacheGet: looking for %u", multi);
|
|
|
|
dlist_foreach(iter, &MXactCache)
|
|
{
|
|
mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
|
|
|
|
if (entry->multi == multi)
|
|
{
|
|
MultiXactMember *ptr;
|
|
Size size;
|
|
|
|
size = sizeof(MultiXactMember) * entry->nmembers;
|
|
ptr = (MultiXactMember *) palloc(size);
|
|
*members = ptr;
|
|
|
|
memcpy(ptr, entry->members, size);
|
|
|
|
debug_elog3(DEBUG2, "CacheGet: found %s",
|
|
mxid_to_string(multi,
|
|
entry->nmembers,
|
|
entry->members));
|
|
|
|
/*
|
|
* Note we modify the list while not using a modifiable iterator.
|
|
* This is acceptable only because we exit the iteration
|
|
* immediately afterwards.
|
|
*/
|
|
dlist_move_head(&MXactCache, iter.cur);
|
|
|
|
return entry->nmembers;
|
|
}
|
|
}
|
|
|
|
debug_elog2(DEBUG2, "CacheGet: not found");
|
|
return -1;
|
|
}
|
|
|
|
/*
|
|
* mXactCachePut
|
|
* Add a new MultiXactId and its composing set into the local cache.
|
|
*/
|
|
static void
|
|
mXactCachePut(MultiXactId multi, int nmembers, MultiXactMember *members)
|
|
{
|
|
mXactCacheEnt *entry;
|
|
|
|
debug_elog3(DEBUG2, "CachePut: storing %s",
|
|
mxid_to_string(multi, nmembers, members));
|
|
|
|
if (MXactContext == NULL)
|
|
{
|
|
/* The cache only lives as long as the current transaction */
|
|
debug_elog2(DEBUG2, "CachePut: initializing memory context");
|
|
MXactContext = AllocSetContextCreate(TopTransactionContext,
|
|
"MultiXact cache context",
|
|
ALLOCSET_SMALL_SIZES);
|
|
}
|
|
|
|
entry = (mXactCacheEnt *)
|
|
MemoryContextAlloc(MXactContext,
|
|
offsetof(mXactCacheEnt, members) +
|
|
nmembers * sizeof(MultiXactMember));
|
|
|
|
entry->multi = multi;
|
|
entry->nmembers = nmembers;
|
|
memcpy(entry->members, members, nmembers * sizeof(MultiXactMember));
|
|
|
|
/* mXactCacheGetBySet assumes the entries are sorted, so sort them */
|
|
qsort(entry->members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
|
|
|
|
dlist_push_head(&MXactCache, &entry->node);
|
|
if (MXactCacheMembers++ >= MAX_CACHE_ENTRIES)
|
|
{
|
|
dlist_node *node;
|
|
mXactCacheEnt *entry;
|
|
|
|
node = dlist_tail_node(&MXactCache);
|
|
dlist_delete(node);
|
|
MXactCacheMembers--;
|
|
|
|
entry = dlist_container(mXactCacheEnt, node, node);
|
|
debug_elog3(DEBUG2, "CachePut: pruning cached multi %u",
|
|
entry->multi);
|
|
|
|
pfree(entry);
|
|
}
|
|
}
|
|
|
|
static char *
|
|
mxstatus_to_string(MultiXactStatus status)
|
|
{
|
|
switch (status)
|
|
{
|
|
case MultiXactStatusForKeyShare:
|
|
return "keysh";
|
|
case MultiXactStatusForShare:
|
|
return "sh";
|
|
case MultiXactStatusForNoKeyUpdate:
|
|
return "fornokeyupd";
|
|
case MultiXactStatusForUpdate:
|
|
return "forupd";
|
|
case MultiXactStatusNoKeyUpdate:
|
|
return "nokeyupd";
|
|
case MultiXactStatusUpdate:
|
|
return "upd";
|
|
default:
|
|
elog(ERROR, "unrecognized multixact status %d", status);
|
|
return "";
|
|
}
|
|
}
|
|
|
|
char *
|
|
mxid_to_string(MultiXactId multi, int nmembers, MultiXactMember *members)
|
|
{
|
|
static char *str = NULL;
|
|
StringInfoData buf;
|
|
int i;
|
|
|
|
if (str != NULL)
|
|
pfree(str);
|
|
|
|
initStringInfo(&buf);
|
|
|
|
appendStringInfo(&buf, "%u %d[%u (%s)", multi, nmembers, members[0].xid,
|
|
mxstatus_to_string(members[0].status));
|
|
|
|
for (i = 1; i < nmembers; i++)
|
|
appendStringInfo(&buf, ", %u (%s)", members[i].xid,
|
|
mxstatus_to_string(members[i].status));
|
|
|
|
appendStringInfoChar(&buf, ']');
|
|
str = MemoryContextStrdup(TopMemoryContext, buf.data);
|
|
pfree(buf.data);
|
|
return str;
|
|
}
|
|
|
|
/*
|
|
* AtEOXact_MultiXact
|
|
* Handle transaction end for MultiXact
|
|
*
|
|
* This is called at top transaction commit or abort (we don't care which).
|
|
*/
|
|
void
|
|
AtEOXact_MultiXact(void)
|
|
{
|
|
/*
|
|
* Reset our OldestMemberMXactId and OldestVisibleMXactId values, both of
|
|
* which should only be valid while within a transaction.
|
|
*
|
|
* We assume that storing a MultiXactId is atomic and so we need not take
|
|
* MultiXactGenLock to do this.
|
|
*/
|
|
OldestMemberMXactId[MyBackendId] = InvalidMultiXactId;
|
|
OldestVisibleMXactId[MyBackendId] = InvalidMultiXactId;
|
|
|
|
/*
|
|
* Discard the local MultiXactId cache. Since MXactContext was created as
|
|
* a child of TopTransactionContext, we needn't delete it explicitly.
|
|
*/
|
|
MXactContext = NULL;
|
|
dlist_init(&MXactCache);
|
|
MXactCacheMembers = 0;
|
|
}
|
|
|
|
/*
|
|
* AtPrepare_MultiXact
|
|
* Save multixact state at 2PC transaction prepare
|
|
*
|
|
* In this phase, we only store our OldestMemberMXactId value in the two-phase
|
|
* state file.
|
|
*/
|
|
void
|
|
AtPrepare_MultiXact(void)
|
|
{
|
|
MultiXactId myOldestMember = OldestMemberMXactId[MyBackendId];
|
|
|
|
if (MultiXactIdIsValid(myOldestMember))
|
|
RegisterTwoPhaseRecord(TWOPHASE_RM_MULTIXACT_ID, 0,
|
|
&myOldestMember, sizeof(MultiXactId));
|
|
}
|
|
|
|
/*
|
|
* PostPrepare_MultiXact
|
|
* Clean up after successful PREPARE TRANSACTION
|
|
*/
|
|
void
|
|
PostPrepare_MultiXact(TransactionId xid)
|
|
{
|
|
MultiXactId myOldestMember;
|
|
|
|
/*
|
|
* Transfer our OldestMemberMXactId value to the slot reserved for the
|
|
* prepared transaction.
|
|
*/
|
|
myOldestMember = OldestMemberMXactId[MyBackendId];
|
|
if (MultiXactIdIsValid(myOldestMember))
|
|
{
|
|
BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid, false);
|
|
|
|
/*
|
|
* Even though storing MultiXactId is atomic, acquire lock to make
|
|
* sure others see both changes, not just the reset of the slot of the
|
|
* current backend. Using a volatile pointer might suffice, but this
|
|
* isn't a hot spot.
|
|
*/
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
|
|
OldestMemberMXactId[dummyBackendId] = myOldestMember;
|
|
OldestMemberMXactId[MyBackendId] = InvalidMultiXactId;
|
|
|
|
LWLockRelease(MultiXactGenLock);
|
|
}
|
|
|
|
/*
|
|
* We don't need to transfer OldestVisibleMXactId value, because the
|
|
* transaction is not going to be looking at any more multixacts once it's
|
|
* prepared.
|
|
*
|
|
* We assume that storing a MultiXactId is atomic and so we need not take
|
|
* MultiXactGenLock to do this.
|
|
*/
|
|
OldestVisibleMXactId[MyBackendId] = InvalidMultiXactId;
|
|
|
|
/*
|
|
* Discard the local MultiXactId cache like in AtEOXact_MultiXact.
|
|
*/
|
|
MXactContext = NULL;
|
|
dlist_init(&MXactCache);
|
|
MXactCacheMembers = 0;
|
|
}
|
|
|
|
/*
|
|
* multixact_twophase_recover
|
|
* Recover the state of a prepared transaction at startup
|
|
*/
|
|
void
|
|
multixact_twophase_recover(TransactionId xid, uint16 info,
|
|
void *recdata, uint32 len)
|
|
{
|
|
BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid, false);
|
|
MultiXactId oldestMember;
|
|
|
|
/*
|
|
* Get the oldest member XID from the state file record, and set it in the
|
|
* OldestMemberMXactId slot reserved for this prepared transaction.
|
|
*/
|
|
Assert(len == sizeof(MultiXactId));
|
|
oldestMember = *((MultiXactId *) recdata);
|
|
|
|
OldestMemberMXactId[dummyBackendId] = oldestMember;
|
|
}
|
|
|
|
/*
|
|
* multixact_twophase_postcommit
|
|
* Similar to AtEOXact_MultiXact but for COMMIT PREPARED
|
|
*/
|
|
void
|
|
multixact_twophase_postcommit(TransactionId xid, uint16 info,
|
|
void *recdata, uint32 len)
|
|
{
|
|
BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid, true);
|
|
|
|
Assert(len == sizeof(MultiXactId));
|
|
|
|
OldestMemberMXactId[dummyBackendId] = InvalidMultiXactId;
|
|
}
|
|
|
|
/*
|
|
* multixact_twophase_postabort
|
|
* This is actually just the same as the COMMIT case.
|
|
*/
|
|
void
|
|
multixact_twophase_postabort(TransactionId xid, uint16 info,
|
|
void *recdata, uint32 len)
|
|
{
|
|
multixact_twophase_postcommit(xid, info, recdata, len);
|
|
}
|
|
|
|
/*
|
|
* Initialization of shared memory for MultiXact. We use two SLRU areas,
|
|
* thus double memory. Also, reserve space for the shared MultiXactState
|
|
* struct and the per-backend MultiXactId arrays (two of those, too).
|
|
*/
|
|
Size
|
|
MultiXactShmemSize(void)
|
|
{
|
|
Size size;
|
|
|
|
/* We need 2*MaxOldestSlot + 1 perBackendXactIds[] entries */
|
|
#define SHARED_MULTIXACT_STATE_SIZE \
|
|
add_size(offsetof(MultiXactStateData, perBackendXactIds) + sizeof(MultiXactId), \
|
|
mul_size(sizeof(MultiXactId) * 2, MaxOldestSlot))
|
|
|
|
size = SHARED_MULTIXACT_STATE_SIZE;
|
|
size = add_size(size, SimpleLruShmemSize(NUM_MULTIXACTOFFSET_BUFFERS, 0));
|
|
size = add_size(size, SimpleLruShmemSize(NUM_MULTIXACTMEMBER_BUFFERS, 0));
|
|
|
|
return size;
|
|
}
|
|
|
|
void
|
|
MultiXactShmemInit(void)
|
|
{
|
|
bool found;
|
|
|
|
debug_elog2(DEBUG2, "Shared Memory Init for MultiXact");
|
|
|
|
MultiXactOffsetCtl->PagePrecedes = MultiXactOffsetPagePrecedes;
|
|
MultiXactMemberCtl->PagePrecedes = MultiXactMemberPagePrecedes;
|
|
|
|
SimpleLruInit(MultiXactOffsetCtl,
|
|
"MultiXactOffset", NUM_MULTIXACTOFFSET_BUFFERS, 0,
|
|
MultiXactOffsetSLRULock, "pg_multixact/offsets",
|
|
LWTRANCHE_MULTIXACTOFFSET_BUFFER,
|
|
SYNC_HANDLER_MULTIXACT_OFFSET);
|
|
SimpleLruInit(MultiXactMemberCtl,
|
|
"MultiXactMember", NUM_MULTIXACTMEMBER_BUFFERS, 0,
|
|
MultiXactMemberSLRULock, "pg_multixact/members",
|
|
LWTRANCHE_MULTIXACTMEMBER_BUFFER,
|
|
SYNC_HANDLER_MULTIXACT_MEMBER);
|
|
|
|
/* Initialize our shared state struct */
|
|
MultiXactState = ShmemInitStruct("Shared MultiXact State",
|
|
SHARED_MULTIXACT_STATE_SIZE,
|
|
&found);
|
|
if (!IsUnderPostmaster)
|
|
{
|
|
Assert(!found);
|
|
|
|
/* Make sure we zero out the per-backend state */
|
|
MemSet(MultiXactState, 0, SHARED_MULTIXACT_STATE_SIZE);
|
|
}
|
|
else
|
|
Assert(found);
|
|
|
|
/*
|
|
* Set up array pointers. Note that perBackendXactIds[0] is wasted space
|
|
* since we only use indexes 1..MaxOldestSlot in each array.
|
|
*/
|
|
OldestMemberMXactId = MultiXactState->perBackendXactIds;
|
|
OldestVisibleMXactId = OldestMemberMXactId + MaxOldestSlot;
|
|
}
|
|
|
|
/*
|
|
* This func must be called ONCE on system install. It creates the initial
|
|
* MultiXact segments. (The MultiXacts directories are assumed to have been
|
|
* created by initdb, and MultiXactShmemInit must have been called already.)
|
|
*/
|
|
void
|
|
BootStrapMultiXact(void)
|
|
{
|
|
int slotno;
|
|
|
|
LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
|
|
|
|
/* Create and zero the first page of the offsets log */
|
|
slotno = ZeroMultiXactOffsetPage(0, false);
|
|
|
|
/* Make sure it's written out */
|
|
SimpleLruWritePage(MultiXactOffsetCtl, slotno);
|
|
Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
|
|
|
|
LWLockRelease(MultiXactOffsetSLRULock);
|
|
|
|
LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
|
|
|
|
/* Create and zero the first page of the members log */
|
|
slotno = ZeroMultiXactMemberPage(0, false);
|
|
|
|
/* Make sure it's written out */
|
|
SimpleLruWritePage(MultiXactMemberCtl, slotno);
|
|
Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
|
|
|
|
LWLockRelease(MultiXactMemberSLRULock);
|
|
}
|
|
|
|
/*
|
|
* Initialize (or reinitialize) a page of MultiXactOffset to zeroes.
|
|
* If writeXlog is true, also emit an XLOG record saying we did this.
|
|
*
|
|
* The page is not actually written, just set up in shared memory.
|
|
* The slot number of the new page is returned.
|
|
*
|
|
* Control lock must be held at entry, and will be held at exit.
|
|
*/
|
|
static int
|
|
ZeroMultiXactOffsetPage(int pageno, bool writeXlog)
|
|
{
|
|
int slotno;
|
|
|
|
slotno = SimpleLruZeroPage(MultiXactOffsetCtl, pageno);
|
|
|
|
if (writeXlog)
|
|
WriteMZeroPageXlogRec(pageno, XLOG_MULTIXACT_ZERO_OFF_PAGE);
|
|
|
|
return slotno;
|
|
}
|
|
|
|
/*
|
|
* Ditto, for MultiXactMember
|
|
*/
|
|
static int
|
|
ZeroMultiXactMemberPage(int pageno, bool writeXlog)
|
|
{
|
|
int slotno;
|
|
|
|
slotno = SimpleLruZeroPage(MultiXactMemberCtl, pageno);
|
|
|
|
if (writeXlog)
|
|
WriteMZeroPageXlogRec(pageno, XLOG_MULTIXACT_ZERO_MEM_PAGE);
|
|
|
|
return slotno;
|
|
}
|
|
|
|
/*
|
|
* MaybeExtendOffsetSlru
|
|
* Extend the offsets SLRU area, if necessary
|
|
*
|
|
* After a binary upgrade from <= 9.2, the pg_multixact/offsets SLRU area might
|
|
* contain files that are shorter than necessary; this would occur if the old
|
|
* installation had used multixacts beyond the first page (files cannot be
|
|
* copied, because the on-disk representation is different). pg_upgrade would
|
|
* update pg_control to set the next offset value to be at that position, so
|
|
* that tuples marked as locked by such MultiXacts would be seen as visible
|
|
* without having to consult multixact. However, trying to create and use a
|
|
* new MultiXactId would result in an error because the page on which the new
|
|
* value would reside does not exist. This routine is in charge of creating
|
|
* such pages.
|
|
*/
|
|
static void
|
|
MaybeExtendOffsetSlru(void)
|
|
{
|
|
int pageno;
|
|
|
|
pageno = MultiXactIdToOffsetPage(MultiXactState->nextMXact);
|
|
|
|
LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
|
|
|
|
if (!SimpleLruDoesPhysicalPageExist(MultiXactOffsetCtl, pageno))
|
|
{
|
|
int slotno;
|
|
|
|
/*
|
|
* Fortunately for us, SimpleLruWritePage is already prepared to deal
|
|
* with creating a new segment file even if the page we're writing is
|
|
* not the first in it, so this is enough.
|
|
*/
|
|
slotno = ZeroMultiXactOffsetPage(pageno, false);
|
|
SimpleLruWritePage(MultiXactOffsetCtl, slotno);
|
|
}
|
|
|
|
LWLockRelease(MultiXactOffsetSLRULock);
|
|
}
|
|
|
|
/*
|
|
* This must be called ONCE during postmaster or standalone-backend startup.
|
|
*
|
|
* StartupXLOG has already established nextMXact/nextOffset by calling
|
|
* MultiXactSetNextMXact and/or MultiXactAdvanceNextMXact, and the oldestMulti
|
|
* info from pg_control and/or MultiXactAdvanceOldest, but we haven't yet
|
|
* replayed WAL.
|
|
*/
|
|
void
|
|
StartupMultiXact(void)
|
|
{
|
|
MultiXactId multi = MultiXactState->nextMXact;
|
|
MultiXactOffset offset = MultiXactState->nextOffset;
|
|
int pageno;
|
|
|
|
/*
|
|
* Initialize offset's idea of the latest page number.
|
|
*/
|
|
pageno = MultiXactIdToOffsetPage(multi);
|
|
MultiXactOffsetCtl->shared->latest_page_number = pageno;
|
|
|
|
/*
|
|
* Initialize member's idea of the latest page number.
|
|
*/
|
|
pageno = MXOffsetToMemberPage(offset);
|
|
MultiXactMemberCtl->shared->latest_page_number = pageno;
|
|
}
|
|
|
|
/*
|
|
* This must be called ONCE at the end of startup/recovery.
|
|
*/
|
|
void
|
|
TrimMultiXact(void)
|
|
{
|
|
MultiXactId nextMXact;
|
|
MultiXactOffset offset;
|
|
MultiXactId oldestMXact;
|
|
Oid oldestMXactDB;
|
|
int pageno;
|
|
int entryno;
|
|
int flagsoff;
|
|
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
nextMXact = MultiXactState->nextMXact;
|
|
offset = MultiXactState->nextOffset;
|
|
oldestMXact = MultiXactState->oldestMultiXactId;
|
|
oldestMXactDB = MultiXactState->oldestMultiXactDB;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
/* Clean up offsets state */
|
|
LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* (Re-)Initialize our idea of the latest page number for offsets.
|
|
*/
|
|
pageno = MultiXactIdToOffsetPage(nextMXact);
|
|
MultiXactOffsetCtl->shared->latest_page_number = pageno;
|
|
|
|
/*
|
|
* Zero out the remainder of the current offsets page. See notes in
|
|
* TrimCLOG() for background. Unlike CLOG, some WAL record covers every
|
|
* pg_multixact SLRU mutation. Since, also unlike CLOG, we ignore the WAL
|
|
* rule "write xlog before data," nextMXact successors may carry obsolete,
|
|
* nonzero offset values. Zero those so case 2 of GetMultiXactIdMembers()
|
|
* operates normally.
|
|
*/
|
|
entryno = MultiXactIdToOffsetEntry(nextMXact);
|
|
if (entryno != 0)
|
|
{
|
|
int slotno;
|
|
MultiXactOffset *offptr;
|
|
|
|
slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, nextMXact);
|
|
offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
|
|
offptr += entryno;
|
|
|
|
MemSet(offptr, 0, BLCKSZ - (entryno * sizeof(MultiXactOffset)));
|
|
|
|
MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
|
|
}
|
|
|
|
LWLockRelease(MultiXactOffsetSLRULock);
|
|
|
|
/* And the same for members */
|
|
LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* (Re-)Initialize our idea of the latest page number for members.
|
|
*/
|
|
pageno = MXOffsetToMemberPage(offset);
|
|
MultiXactMemberCtl->shared->latest_page_number = pageno;
|
|
|
|
/*
|
|
* Zero out the remainder of the current members page. See notes in
|
|
* TrimCLOG() for motivation.
|
|
*/
|
|
flagsoff = MXOffsetToFlagsOffset(offset);
|
|
if (flagsoff != 0)
|
|
{
|
|
int slotno;
|
|
TransactionId *xidptr;
|
|
int memberoff;
|
|
|
|
memberoff = MXOffsetToMemberOffset(offset);
|
|
slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, offset);
|
|
xidptr = (TransactionId *)
|
|
(MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
|
|
|
|
MemSet(xidptr, 0, BLCKSZ - memberoff);
|
|
|
|
/*
|
|
* Note: we don't need to zero out the flag bits in the remaining
|
|
* members of the current group, because they are always reset before
|
|
* writing.
|
|
*/
|
|
|
|
MultiXactMemberCtl->shared->page_dirty[slotno] = true;
|
|
}
|
|
|
|
LWLockRelease(MultiXactMemberSLRULock);
|
|
|
|
/* signal that we're officially up */
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
MultiXactState->finishedStartup = true;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
/* Now compute how far away the next members wraparound is. */
|
|
SetMultiXactIdLimit(oldestMXact, oldestMXactDB, true);
|
|
}
|
|
|
|
/*
|
|
* Get the MultiXact data to save in a checkpoint record
|
|
*/
|
|
void
|
|
MultiXactGetCheckptMulti(bool is_shutdown,
|
|
MultiXactId *nextMulti,
|
|
MultiXactOffset *nextMultiOffset,
|
|
MultiXactId *oldestMulti,
|
|
Oid *oldestMultiDB)
|
|
{
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
*nextMulti = MultiXactState->nextMXact;
|
|
*nextMultiOffset = MultiXactState->nextOffset;
|
|
*oldestMulti = MultiXactState->oldestMultiXactId;
|
|
*oldestMultiDB = MultiXactState->oldestMultiXactDB;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
debug_elog6(DEBUG2,
|
|
"MultiXact: checkpoint is nextMulti %u, nextOffset %u, oldestMulti %u in DB %u",
|
|
*nextMulti, *nextMultiOffset, *oldestMulti, *oldestMultiDB);
|
|
}
|
|
|
|
/*
|
|
* Perform a checkpoint --- either during shutdown, or on-the-fly
|
|
*/
|
|
void
|
|
CheckPointMultiXact(void)
|
|
{
|
|
TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(true);
|
|
|
|
/*
|
|
* Write dirty MultiXact pages to disk. This may result in sync requests
|
|
* queued for later handling by ProcessSyncRequests(), as part of the
|
|
* checkpoint.
|
|
*/
|
|
SimpleLruWriteAll(MultiXactOffsetCtl, true);
|
|
SimpleLruWriteAll(MultiXactMemberCtl, true);
|
|
|
|
TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_DONE(true);
|
|
}
|
|
|
|
/*
|
|
* Set the next-to-be-assigned MultiXactId and offset
|
|
*
|
|
* This is used when we can determine the correct next ID/offset exactly
|
|
* from a checkpoint record. Although this is only called during bootstrap
|
|
* and XLog replay, we take the lock in case any hot-standby backends are
|
|
* examining the values.
|
|
*/
|
|
void
|
|
MultiXactSetNextMXact(MultiXactId nextMulti,
|
|
MultiXactOffset nextMultiOffset)
|
|
{
|
|
debug_elog4(DEBUG2, "MultiXact: setting next multi to %u offset %u",
|
|
nextMulti, nextMultiOffset);
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
MultiXactState->nextMXact = nextMulti;
|
|
MultiXactState->nextOffset = nextMultiOffset;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
/*
|
|
* During a binary upgrade, make sure that the offsets SLRU is large
|
|
* enough to contain the next value that would be created.
|
|
*
|
|
* We need to do this pretty early during the first startup in binary
|
|
* upgrade mode: before StartupMultiXact() in fact, because this routine
|
|
* is called even before that by StartupXLOG(). And we can't do it
|
|
* earlier than at this point, because during that first call of this
|
|
* routine we determine the MultiXactState->nextMXact value that
|
|
* MaybeExtendOffsetSlru needs.
|
|
*/
|
|
if (IsBinaryUpgrade)
|
|
MaybeExtendOffsetSlru();
|
|
}
|
|
|
|
/*
|
|
* Determine the last safe MultiXactId to allocate given the currently oldest
|
|
* datminmxid (ie, the oldest MultiXactId that might exist in any database
|
|
* of our cluster), and the OID of the (or a) database with that value.
|
|
*
|
|
* is_startup is true when we are just starting the cluster, false when we
|
|
* are updating state in a running cluster. This only affects log messages.
|
|
*/
|
|
void
|
|
SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
|
|
bool is_startup)
|
|
{
|
|
MultiXactId multiVacLimit;
|
|
MultiXactId multiWarnLimit;
|
|
MultiXactId multiStopLimit;
|
|
MultiXactId multiWrapLimit;
|
|
MultiXactId curMulti;
|
|
bool needs_offset_vacuum;
|
|
|
|
Assert(MultiXactIdIsValid(oldest_datminmxid));
|
|
|
|
/*
|
|
* We pretend that a wrap will happen halfway through the multixact ID
|
|
* space, but that's not really true, because multixacts wrap differently
|
|
* from transaction IDs. Note that, separately from any concern about
|
|
* multixact IDs wrapping, we must ensure that multixact members do not
|
|
* wrap. Limits for that are set in SetOffsetVacuumLimit, not here.
|
|
*/
|
|
multiWrapLimit = oldest_datminmxid + (MaxMultiXactId >> 1);
|
|
if (multiWrapLimit < FirstMultiXactId)
|
|
multiWrapLimit += FirstMultiXactId;
|
|
|
|
/*
|
|
* We'll refuse to continue assigning MultiXactIds once we get within 3M
|
|
* multi of data loss. See SetTransactionIdLimit.
|
|
*/
|
|
multiStopLimit = multiWrapLimit - 3000000;
|
|
if (multiStopLimit < FirstMultiXactId)
|
|
multiStopLimit -= FirstMultiXactId;
|
|
|
|
/*
|
|
* We'll start complaining loudly when we get within 40M multis of data
|
|
* loss. This is kind of arbitrary, but if you let your gas gauge get
|
|
* down to 2% of full, would you be looking for the next gas station? We
|
|
* need to be fairly liberal about this number because there are lots of
|
|
* scenarios where most transactions are done by automatic clients that
|
|
* won't pay attention to warnings. (No, we're not gonna make this
|
|
* configurable. If you know enough to configure it, you know enough to
|
|
* not get in this kind of trouble in the first place.)
|
|
*/
|
|
multiWarnLimit = multiWrapLimit - 40000000;
|
|
if (multiWarnLimit < FirstMultiXactId)
|
|
multiWarnLimit -= FirstMultiXactId;
|
|
|
|
/*
|
|
* We'll start trying to force autovacuums when oldest_datminmxid gets to
|
|
* be more than autovacuum_multixact_freeze_max_age mxids old.
|
|
*
|
|
* Note: autovacuum_multixact_freeze_max_age is a PGC_POSTMASTER parameter
|
|
* so that we don't have to worry about dealing with on-the-fly changes in
|
|
* its value. See SetTransactionIdLimit.
|
|
*/
|
|
multiVacLimit = oldest_datminmxid + autovacuum_multixact_freeze_max_age;
|
|
if (multiVacLimit < FirstMultiXactId)
|
|
multiVacLimit += FirstMultiXactId;
|
|
|
|
/* Grab lock for just long enough to set the new limit values */
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
MultiXactState->oldestMultiXactId = oldest_datminmxid;
|
|
MultiXactState->oldestMultiXactDB = oldest_datoid;
|
|
MultiXactState->multiVacLimit = multiVacLimit;
|
|
MultiXactState->multiWarnLimit = multiWarnLimit;
|
|
MultiXactState->multiStopLimit = multiStopLimit;
|
|
MultiXactState->multiWrapLimit = multiWrapLimit;
|
|
curMulti = MultiXactState->nextMXact;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
/* Log the info */
|
|
ereport(DEBUG1,
|
|
(errmsg("MultiXactId wrap limit is %u, limited by database with OID %u",
|
|
multiWrapLimit, oldest_datoid)));
|
|
|
|
/*
|
|
* Computing the actual limits is only possible once the data directory is
|
|
* in a consistent state. There's no need to compute the limits while
|
|
* still replaying WAL - no decisions about new multis are made even
|
|
* though multixact creations might be replayed. So we'll only do further
|
|
* checks after TrimMultiXact() has been called.
|
|
*/
|
|
if (!MultiXactState->finishedStartup)
|
|
return;
|
|
|
|
Assert(!InRecovery);
|
|
|
|
/* Set limits for offset vacuum. */
|
|
needs_offset_vacuum = SetOffsetVacuumLimit(is_startup);
|
|
|
|
/*
|
|
* If past the autovacuum force point, immediately signal an autovac
|
|
* request. The reason for this is that autovac only processes one
|
|
* database per invocation. Once it's finished cleaning up the oldest
|
|
* database, it'll call here, and we'll signal the postmaster to start
|
|
* another iteration immediately if there are still any old databases.
|
|
*/
|
|
if ((MultiXactIdPrecedes(multiVacLimit, curMulti) ||
|
|
needs_offset_vacuum) && IsUnderPostmaster)
|
|
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
|
|
|
|
/* Give an immediate warning if past the wrap warn point */
|
|
if (MultiXactIdPrecedes(multiWarnLimit, curMulti))
|
|
{
|
|
char *oldest_datname;
|
|
|
|
/*
|
|
* We can be called when not inside a transaction, for example during
|
|
* StartupXLOG(). In such a case we cannot do database access, so we
|
|
* must just report the oldest DB's OID.
|
|
*
|
|
* Note: it's also possible that get_database_name fails and returns
|
|
* NULL, for example because the database just got dropped. We'll
|
|
* still warn, even though the warning might now be unnecessary.
|
|
*/
|
|
if (IsTransactionState())
|
|
oldest_datname = get_database_name(oldest_datoid);
|
|
else
|
|
oldest_datname = NULL;
|
|
|
|
if (oldest_datname)
|
|
ereport(WARNING,
|
|
(errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
|
|
"database \"%s\" must be vacuumed before %u more MultiXactIds are used",
|
|
multiWrapLimit - curMulti,
|
|
oldest_datname,
|
|
multiWrapLimit - curMulti),
|
|
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
|
|
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
|
|
else
|
|
ereport(WARNING,
|
|
(errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
|
|
"database with OID %u must be vacuumed before %u more MultiXactIds are used",
|
|
multiWrapLimit - curMulti,
|
|
oldest_datoid,
|
|
multiWrapLimit - curMulti),
|
|
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
|
|
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Ensure the next-to-be-assigned MultiXactId is at least minMulti,
|
|
* and similarly nextOffset is at least minMultiOffset.
|
|
*
|
|
* This is used when we can determine minimum safe values from an XLog
|
|
* record (either an on-line checkpoint or an mxact creation log entry).
|
|
* Although this is only called during XLog replay, we take the lock in case
|
|
* any hot-standby backends are examining the values.
|
|
*/
|
|
void
|
|
MultiXactAdvanceNextMXact(MultiXactId minMulti,
|
|
MultiXactOffset minMultiOffset)
|
|
{
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
if (MultiXactIdPrecedes(MultiXactState->nextMXact, minMulti))
|
|
{
|
|
debug_elog3(DEBUG2, "MultiXact: setting next multi to %u", minMulti);
|
|
MultiXactState->nextMXact = minMulti;
|
|
}
|
|
if (MultiXactOffsetPrecedes(MultiXactState->nextOffset, minMultiOffset))
|
|
{
|
|
debug_elog3(DEBUG2, "MultiXact: setting next offset to %u",
|
|
minMultiOffset);
|
|
MultiXactState->nextOffset = minMultiOffset;
|
|
}
|
|
LWLockRelease(MultiXactGenLock);
|
|
}
|
|
|
|
/*
|
|
* Update our oldestMultiXactId value, but only if it's more recent than what
|
|
* we had.
|
|
*
|
|
* This may only be called during WAL replay.
|
|
*/
|
|
void
|
|
MultiXactAdvanceOldest(MultiXactId oldestMulti, Oid oldestMultiDB)
|
|
{
|
|
Assert(InRecovery);
|
|
|
|
if (MultiXactIdPrecedes(MultiXactState->oldestMultiXactId, oldestMulti))
|
|
SetMultiXactIdLimit(oldestMulti, oldestMultiDB, false);
|
|
}
|
|
|
|
/*
|
|
* Make sure that MultiXactOffset has room for a newly-allocated MultiXactId.
|
|
*
|
|
* NB: this is called while holding MultiXactGenLock. We want it to be very
|
|
* fast most of the time; even when it's not so fast, no actual I/O need
|
|
* happen unless we're forced to write out a dirty log or xlog page to make
|
|
* room in shared memory.
|
|
*/
|
|
static void
|
|
ExtendMultiXactOffset(MultiXactId multi)
|
|
{
|
|
int pageno;
|
|
|
|
/*
|
|
* No work except at first MultiXactId of a page. But beware: just after
|
|
* wraparound, the first MultiXactId of page zero is FirstMultiXactId.
|
|
*/
|
|
if (MultiXactIdToOffsetEntry(multi) != 0 &&
|
|
multi != FirstMultiXactId)
|
|
return;
|
|
|
|
pageno = MultiXactIdToOffsetPage(multi);
|
|
|
|
LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
|
|
|
|
/* Zero the page and make an XLOG entry about it */
|
|
ZeroMultiXactOffsetPage(pageno, true);
|
|
|
|
LWLockRelease(MultiXactOffsetSLRULock);
|
|
}
|
|
|
|
/*
|
|
* Make sure that MultiXactMember has room for the members of a newly-
|
|
* allocated MultiXactId.
|
|
*
|
|
* Like the above routine, this is called while holding MultiXactGenLock;
|
|
* same comments apply.
|
|
*/
|
|
static void
|
|
ExtendMultiXactMember(MultiXactOffset offset, int nmembers)
|
|
{
|
|
/*
|
|
* It's possible that the members span more than one page of the members
|
|
* file, so we loop to ensure we consider each page. The coding is not
|
|
* optimal if the members span several pages, but that seems unusual
|
|
* enough to not worry much about.
|
|
*/
|
|
while (nmembers > 0)
|
|
{
|
|
int flagsoff;
|
|
int flagsbit;
|
|
uint32 difference;
|
|
|
|
/*
|
|
* Only zero when at first entry of a page.
|
|
*/
|
|
flagsoff = MXOffsetToFlagsOffset(offset);
|
|
flagsbit = MXOffsetToFlagsBitShift(offset);
|
|
if (flagsoff == 0 && flagsbit == 0)
|
|
{
|
|
int pageno;
|
|
|
|
pageno = MXOffsetToMemberPage(offset);
|
|
|
|
LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
|
|
|
|
/* Zero the page and make an XLOG entry about it */
|
|
ZeroMultiXactMemberPage(pageno, true);
|
|
|
|
LWLockRelease(MultiXactMemberSLRULock);
|
|
}
|
|
|
|
/*
|
|
* Compute the number of items till end of current page. Careful: if
|
|
* addition of unsigned ints wraps around, we're at the last page of
|
|
* the last segment; since that page holds a different number of items
|
|
* than other pages, we need to do it differently.
|
|
*/
|
|
if (offset + MAX_MEMBERS_IN_LAST_MEMBERS_PAGE < offset)
|
|
{
|
|
/*
|
|
* This is the last page of the last segment; we can compute the
|
|
* number of items left to allocate in it without modulo
|
|
* arithmetic.
|
|
*/
|
|
difference = MaxMultiXactOffset - offset + 1;
|
|
}
|
|
else
|
|
difference = MULTIXACT_MEMBERS_PER_PAGE - offset % MULTIXACT_MEMBERS_PER_PAGE;
|
|
|
|
/*
|
|
* Advance to next page, taking care to properly handle the wraparound
|
|
* case. OK if nmembers goes negative.
|
|
*/
|
|
nmembers -= difference;
|
|
offset += difference;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* GetOldestMultiXactId
|
|
*
|
|
* Return the oldest MultiXactId that's still possibly still seen as live by
|
|
* any running transaction. Older ones might still exist on disk, but they no
|
|
* longer have any running member transaction.
|
|
*
|
|
* It's not safe to truncate MultiXact SLRU segments on the value returned by
|
|
* this function; however, it can be used by a full-table vacuum to set the
|
|
* point at which it will be possible to truncate SLRU for that table.
|
|
*/
|
|
MultiXactId
|
|
GetOldestMultiXactId(void)
|
|
{
|
|
MultiXactId oldestMXact;
|
|
MultiXactId nextMXact;
|
|
int i;
|
|
|
|
/*
|
|
* This is the oldest valid value among all the OldestMemberMXactId[] and
|
|
* OldestVisibleMXactId[] entries, or nextMXact if none are valid.
|
|
*/
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
|
|
/*
|
|
* We have to beware of the possibility that nextMXact is in the
|
|
* wrapped-around state. We don't fix the counter itself here, but we
|
|
* must be sure to use a valid value in our calculation.
|
|
*/
|
|
nextMXact = MultiXactState->nextMXact;
|
|
if (nextMXact < FirstMultiXactId)
|
|
nextMXact = FirstMultiXactId;
|
|
|
|
oldestMXact = nextMXact;
|
|
for (i = 1; i <= MaxOldestSlot; i++)
|
|
{
|
|
MultiXactId thisoldest;
|
|
|
|
thisoldest = OldestMemberMXactId[i];
|
|
if (MultiXactIdIsValid(thisoldest) &&
|
|
MultiXactIdPrecedes(thisoldest, oldestMXact))
|
|
oldestMXact = thisoldest;
|
|
thisoldest = OldestVisibleMXactId[i];
|
|
if (MultiXactIdIsValid(thisoldest) &&
|
|
MultiXactIdPrecedes(thisoldest, oldestMXact))
|
|
oldestMXact = thisoldest;
|
|
}
|
|
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
return oldestMXact;
|
|
}
|
|
|
|
/*
|
|
* Determine how aggressively we need to vacuum in order to prevent member
|
|
* wraparound.
|
|
*
|
|
* To do so determine what's the oldest member offset and install the limit
|
|
* info in MultiXactState, where it can be used to prevent overrun of old data
|
|
* in the members SLRU area.
|
|
*
|
|
* The return value is true if emergency autovacuum is required and false
|
|
* otherwise.
|
|
*/
|
|
static bool
|
|
SetOffsetVacuumLimit(bool is_startup)
|
|
{
|
|
MultiXactId oldestMultiXactId;
|
|
MultiXactId nextMXact;
|
|
MultiXactOffset oldestOffset = 0; /* placate compiler */
|
|
MultiXactOffset prevOldestOffset;
|
|
MultiXactOffset nextOffset;
|
|
bool oldestOffsetKnown = false;
|
|
bool prevOldestOffsetKnown;
|
|
MultiXactOffset offsetStopLimit = 0;
|
|
MultiXactOffset prevOffsetStopLimit;
|
|
|
|
/*
|
|
* NB: Have to prevent concurrent truncation, we might otherwise try to
|
|
* lookup an oldestMulti that's concurrently getting truncated away.
|
|
*/
|
|
LWLockAcquire(MultiXactTruncationLock, LW_SHARED);
|
|
|
|
/* Read relevant fields from shared memory. */
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
oldestMultiXactId = MultiXactState->oldestMultiXactId;
|
|
nextMXact = MultiXactState->nextMXact;
|
|
nextOffset = MultiXactState->nextOffset;
|
|
prevOldestOffsetKnown = MultiXactState->oldestOffsetKnown;
|
|
prevOldestOffset = MultiXactState->oldestOffset;
|
|
prevOffsetStopLimit = MultiXactState->offsetStopLimit;
|
|
Assert(MultiXactState->finishedStartup);
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
/*
|
|
* Determine the offset of the oldest multixact. Normally, we can read
|
|
* the offset from the multixact itself, but there's an important special
|
|
* case: if there are no multixacts in existence at all, oldestMXact
|
|
* obviously can't point to one. It will instead point to the multixact
|
|
* ID that will be assigned the next time one is needed.
|
|
*/
|
|
if (oldestMultiXactId == nextMXact)
|
|
{
|
|
/*
|
|
* When the next multixact gets created, it will be stored at the next
|
|
* offset.
|
|
*/
|
|
oldestOffset = nextOffset;
|
|
oldestOffsetKnown = true;
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Figure out where the oldest existing multixact's offsets are
|
|
* stored. Due to bugs in early release of PostgreSQL 9.3.X and 9.4.X,
|
|
* the supposedly-earliest multixact might not really exist. We are
|
|
* careful not to fail in that case.
|
|
*/
|
|
oldestOffsetKnown =
|
|
find_multixact_start(oldestMultiXactId, &oldestOffset);
|
|
|
|
if (oldestOffsetKnown)
|
|
ereport(DEBUG1,
|
|
(errmsg("oldest MultiXactId member is at offset %u",
|
|
oldestOffset)));
|
|
else
|
|
ereport(LOG,
|
|
(errmsg("MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact %u does not exist on disk",
|
|
oldestMultiXactId)));
|
|
}
|
|
|
|
LWLockRelease(MultiXactTruncationLock);
|
|
|
|
/*
|
|
* If we can, compute limits (and install them MultiXactState) to prevent
|
|
* overrun of old data in the members SLRU area. We can only do so if the
|
|
* oldest offset is known though.
|
|
*/
|
|
if (oldestOffsetKnown)
|
|
{
|
|
/* move back to start of the corresponding segment */
|
|
offsetStopLimit = oldestOffset - (oldestOffset %
|
|
(MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT));
|
|
|
|
/* always leave one segment before the wraparound point */
|
|
offsetStopLimit -= (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT);
|
|
|
|
if (!prevOldestOffsetKnown && !is_startup)
|
|
ereport(LOG,
|
|
(errmsg("MultiXact member wraparound protections are now enabled")));
|
|
|
|
ereport(DEBUG1,
|
|
(errmsg("MultiXact member stop limit is now %u based on MultiXact %u",
|
|
offsetStopLimit, oldestMultiXactId)));
|
|
}
|
|
else if (prevOldestOffsetKnown)
|
|
{
|
|
/*
|
|
* If we failed to get the oldest offset this time, but we have a
|
|
* value from a previous pass through this function, use the old
|
|
* values rather than automatically forcing an emergency autovacuum
|
|
* cycle again.
|
|
*/
|
|
oldestOffset = prevOldestOffset;
|
|
oldestOffsetKnown = true;
|
|
offsetStopLimit = prevOffsetStopLimit;
|
|
}
|
|
|
|
/* Install the computed values */
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
MultiXactState->oldestOffset = oldestOffset;
|
|
MultiXactState->oldestOffsetKnown = oldestOffsetKnown;
|
|
MultiXactState->offsetStopLimit = offsetStopLimit;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
/*
|
|
* Do we need an emergency autovacuum? If we're not sure, assume yes.
|
|
*/
|
|
return !oldestOffsetKnown ||
|
|
(nextOffset - oldestOffset > MULTIXACT_MEMBER_SAFE_THRESHOLD);
|
|
}
|
|
|
|
/*
|
|
* Return whether adding "distance" to "start" would move past "boundary".
|
|
*
|
|
* We use this to determine whether the addition is "wrapping around" the
|
|
* boundary point, hence the name. The reason we don't want to use the regular
|
|
* 2^31-modulo arithmetic here is that we want to be able to use the whole of
|
|
* the 2^32-1 space here, allowing for more multixacts than would fit
|
|
* otherwise.
|
|
*/
|
|
static bool
|
|
MultiXactOffsetWouldWrap(MultiXactOffset boundary, MultiXactOffset start,
|
|
uint32 distance)
|
|
{
|
|
MultiXactOffset finish;
|
|
|
|
/*
|
|
* Note that offset number 0 is not used (see GetMultiXactIdMembers), so
|
|
* if the addition wraps around the UINT_MAX boundary, skip that value.
|
|
*/
|
|
finish = start + distance;
|
|
if (finish < start)
|
|
finish++;
|
|
|
|
/*-----------------------------------------------------------------------
|
|
* When the boundary is numerically greater than the starting point, any
|
|
* value numerically between the two is not wrapped:
|
|
*
|
|
* <----S----B---->
|
|
* [---) = F wrapped past B (and UINT_MAX)
|
|
* [---) = F not wrapped
|
|
* [----] = F wrapped past B
|
|
*
|
|
* When the boundary is numerically less than the starting point (i.e. the
|
|
* UINT_MAX wraparound occurs somewhere in between) then all values in
|
|
* between are wrapped:
|
|
*
|
|
* <----B----S---->
|
|
* [---) = F not wrapped past B (but wrapped past UINT_MAX)
|
|
* [---) = F wrapped past B (and UINT_MAX)
|
|
* [----] = F not wrapped
|
|
*-----------------------------------------------------------------------
|
|
*/
|
|
if (start < boundary)
|
|
return finish >= boundary || finish < start;
|
|
else
|
|
return finish >= boundary && finish < start;
|
|
}
|
|
|
|
/*
|
|
* Find the starting offset of the given MultiXactId.
|
|
*
|
|
* Returns false if the file containing the multi does not exist on disk.
|
|
* Otherwise, returns true and sets *result to the starting member offset.
|
|
*
|
|
* This function does not prevent concurrent truncation, so if that's
|
|
* required, the caller has to protect against that.
|
|
*/
|
|
static bool
|
|
find_multixact_start(MultiXactId multi, MultiXactOffset *result)
|
|
{
|
|
MultiXactOffset offset;
|
|
int pageno;
|
|
int entryno;
|
|
int slotno;
|
|
MultiXactOffset *offptr;
|
|
|
|
Assert(MultiXactState->finishedStartup);
|
|
|
|
pageno = MultiXactIdToOffsetPage(multi);
|
|
entryno = MultiXactIdToOffsetEntry(multi);
|
|
|
|
/*
|
|
* Write out dirty data, so PhysicalPageExists can work correctly.
|
|
*/
|
|
SimpleLruWriteAll(MultiXactOffsetCtl, true);
|
|
SimpleLruWriteAll(MultiXactMemberCtl, true);
|
|
|
|
if (!SimpleLruDoesPhysicalPageExist(MultiXactOffsetCtl, pageno))
|
|
return false;
|
|
|
|
/* lock is acquired by SimpleLruReadPage_ReadOnly */
|
|
slotno = SimpleLruReadPage_ReadOnly(MultiXactOffsetCtl, pageno, multi);
|
|
offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
|
|
offptr += entryno;
|
|
offset = *offptr;
|
|
LWLockRelease(MultiXactOffsetSLRULock);
|
|
|
|
*result = offset;
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Determine how many multixacts, and how many multixact members, currently
|
|
* exist. Return false if unable to determine.
|
|
*/
|
|
static bool
|
|
ReadMultiXactCounts(uint32 *multixacts, MultiXactOffset *members)
|
|
{
|
|
MultiXactOffset nextOffset;
|
|
MultiXactOffset oldestOffset;
|
|
MultiXactId oldestMultiXactId;
|
|
MultiXactId nextMultiXactId;
|
|
bool oldestOffsetKnown;
|
|
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
nextOffset = MultiXactState->nextOffset;
|
|
oldestMultiXactId = MultiXactState->oldestMultiXactId;
|
|
nextMultiXactId = MultiXactState->nextMXact;
|
|
oldestOffset = MultiXactState->oldestOffset;
|
|
oldestOffsetKnown = MultiXactState->oldestOffsetKnown;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
if (!oldestOffsetKnown)
|
|
return false;
|
|
|
|
*members = nextOffset - oldestOffset;
|
|
*multixacts = nextMultiXactId - oldestMultiXactId;
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Multixact members can be removed once the multixacts that refer to them
|
|
* are older than every datminmxid. autovacuum_multixact_freeze_max_age and
|
|
* vacuum_multixact_freeze_table_age work together to make sure we never have
|
|
* too many multixacts; we hope that, at least under normal circumstances,
|
|
* this will also be sufficient to keep us from using too many offsets.
|
|
* However, if the average multixact has many members, we might exhaust the
|
|
* members space while still using few enough members that these limits fail
|
|
* to trigger full table scans for relminmxid advancement. At that point,
|
|
* we'd have no choice but to start failing multixact-creating operations
|
|
* with an error.
|
|
*
|
|
* To prevent that, if more than a threshold portion of the members space is
|
|
* used, we effectively reduce autovacuum_multixact_freeze_max_age and
|
|
* to a value just less than the number of multixacts in use. We hope that
|
|
* this will quickly trigger autovacuuming on the table or tables with the
|
|
* oldest relminmxid, thus allowing datminmxid values to advance and removing
|
|
* some members.
|
|
*
|
|
* As the fraction of the member space currently in use grows, we become
|
|
* more aggressive in clamping this value. That not only causes autovacuum
|
|
* to ramp up, but also makes any manual vacuums the user issues more
|
|
* aggressive. This happens because vacuum_set_xid_limits() clamps the
|
|
* freeze table and the minimum freeze age based on the effective
|
|
* autovacuum_multixact_freeze_max_age this function returns. In the worst
|
|
* case, we'll claim the freeze_max_age to zero, and every vacuum of any
|
|
* table will try to freeze every multixact.
|
|
*
|
|
* It's possible that these thresholds should be user-tunable, but for now
|
|
* we keep it simple.
|
|
*/
|
|
int
|
|
MultiXactMemberFreezeThreshold(void)
|
|
{
|
|
MultiXactOffset members;
|
|
uint32 multixacts;
|
|
uint32 victim_multixacts;
|
|
double fraction;
|
|
|
|
/* If we can't determine member space utilization, assume the worst. */
|
|
if (!ReadMultiXactCounts(&multixacts, &members))
|
|
return 0;
|
|
|
|
/* If member space utilization is low, no special action is required. */
|
|
if (members <= MULTIXACT_MEMBER_SAFE_THRESHOLD)
|
|
return autovacuum_multixact_freeze_max_age;
|
|
|
|
/*
|
|
* Compute a target for relminmxid advancement. The number of multixacts
|
|
* we try to eliminate from the system is based on how far we are past
|
|
* MULTIXACT_MEMBER_SAFE_THRESHOLD.
|
|
*/
|
|
fraction = (double) (members - MULTIXACT_MEMBER_SAFE_THRESHOLD) /
|
|
(MULTIXACT_MEMBER_DANGER_THRESHOLD - MULTIXACT_MEMBER_SAFE_THRESHOLD);
|
|
victim_multixacts = multixacts * fraction;
|
|
|
|
/* fraction could be > 1.0, but lowest possible freeze age is zero */
|
|
if (victim_multixacts > multixacts)
|
|
return 0;
|
|
return multixacts - victim_multixacts;
|
|
}
|
|
|
|
typedef struct mxtruncinfo
|
|
{
|
|
int earliestExistingPage;
|
|
} mxtruncinfo;
|
|
|
|
/*
|
|
* SlruScanDirectory callback
|
|
* This callback determines the earliest existing page number.
|
|
*/
|
|
static bool
|
|
SlruScanDirCbFindEarliest(SlruCtl ctl, char *filename, int segpage, void *data)
|
|
{
|
|
mxtruncinfo *trunc = (mxtruncinfo *) data;
|
|
|
|
if (trunc->earliestExistingPage == -1 ||
|
|
ctl->PagePrecedes(segpage, trunc->earliestExistingPage))
|
|
{
|
|
trunc->earliestExistingPage = segpage;
|
|
}
|
|
|
|
return false; /* keep going */
|
|
}
|
|
|
|
|
|
/*
|
|
* Delete members segments [oldest, newOldest)
|
|
*
|
|
* The members SLRU can, in contrast to the offsets one, be filled to almost
|
|
* the full range at once. This means SimpleLruTruncate() can't trivially be
|
|
* used - instead the to-be-deleted range is computed using the offsets
|
|
* SLRU. C.f. TruncateMultiXact().
|
|
*/
|
|
static void
|
|
PerformMembersTruncation(MultiXactOffset oldestOffset, MultiXactOffset newOldestOffset)
|
|
{
|
|
const int maxsegment = MXOffsetToMemberSegment(MaxMultiXactOffset);
|
|
int startsegment = MXOffsetToMemberSegment(oldestOffset);
|
|
int endsegment = MXOffsetToMemberSegment(newOldestOffset);
|
|
int segment = startsegment;
|
|
|
|
/*
|
|
* Delete all the segments but the last one. The last segment can still
|
|
* contain, possibly partially, valid data.
|
|
*/
|
|
while (segment != endsegment)
|
|
{
|
|
elog(DEBUG2, "truncating multixact members segment %x", segment);
|
|
SlruDeleteSegment(MultiXactMemberCtl, segment);
|
|
|
|
/* move to next segment, handling wraparound correctly */
|
|
if (segment == maxsegment)
|
|
segment = 0;
|
|
else
|
|
segment += 1;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Delete offsets segments [oldest, newOldest)
|
|
*/
|
|
static void
|
|
PerformOffsetsTruncation(MultiXactId oldestMulti, MultiXactId newOldestMulti)
|
|
{
|
|
/*
|
|
* We step back one multixact to avoid passing a cutoff page that hasn't
|
|
* been created yet in the rare case that oldestMulti would be the first
|
|
* item on a page and oldestMulti == nextMulti. In that case, if we
|
|
* didn't subtract one, we'd trigger SimpleLruTruncate's wraparound
|
|
* detection.
|
|
*/
|
|
SimpleLruTruncate(MultiXactOffsetCtl,
|
|
MultiXactIdToOffsetPage(PreviousMultiXactId(newOldestMulti)));
|
|
}
|
|
|
|
/*
|
|
* Remove all MultiXactOffset and MultiXactMember segments before the oldest
|
|
* ones still of interest.
|
|
*
|
|
* This is only called on a primary as part of vacuum (via
|
|
* vac_truncate_clog()). During recovery truncation is done by replaying
|
|
* truncation WAL records logged here.
|
|
*
|
|
* newOldestMulti is the oldest currently required multixact, newOldestMultiDB
|
|
* is one of the databases preventing newOldestMulti from increasing.
|
|
*/
|
|
void
|
|
TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB)
|
|
{
|
|
MultiXactId oldestMulti;
|
|
MultiXactId nextMulti;
|
|
MultiXactOffset newOldestOffset;
|
|
MultiXactOffset oldestOffset;
|
|
MultiXactOffset nextOffset;
|
|
mxtruncinfo trunc;
|
|
MultiXactId earliest;
|
|
|
|
Assert(!RecoveryInProgress());
|
|
Assert(MultiXactState->finishedStartup);
|
|
|
|
/*
|
|
* We can only allow one truncation to happen at once. Otherwise parts of
|
|
* members might vanish while we're doing lookups or similar. There's no
|
|
* need to have an interlock with creating new multis or such, since those
|
|
* are constrained by the limits (which only grow, never shrink).
|
|
*/
|
|
LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
|
|
|
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
|
nextMulti = MultiXactState->nextMXact;
|
|
nextOffset = MultiXactState->nextOffset;
|
|
oldestMulti = MultiXactState->oldestMultiXactId;
|
|
LWLockRelease(MultiXactGenLock);
|
|
Assert(MultiXactIdIsValid(oldestMulti));
|
|
|
|
/*
|
|
* Make sure to only attempt truncation if there's values to truncate
|
|
* away. In normal processing values shouldn't go backwards, but there's
|
|
* some corner cases (due to bugs) where that's possible.
|
|
*/
|
|
if (MultiXactIdPrecedesOrEquals(newOldestMulti, oldestMulti))
|
|
{
|
|
LWLockRelease(MultiXactTruncationLock);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Note we can't just plow ahead with the truncation; it's possible that
|
|
* there are no segments to truncate, which is a problem because we are
|
|
* going to attempt to read the offsets page to determine where to
|
|
* truncate the members SLRU. So we first scan the directory to determine
|
|
* the earliest offsets page number that we can read without error.
|
|
*
|
|
* NB: It's also possible that the page that oldestMulti is on has already
|
|
* been truncated away, and we crashed before updating oldestMulti.
|
|
*/
|
|
trunc.earliestExistingPage = -1;
|
|
SlruScanDirectory(MultiXactOffsetCtl, SlruScanDirCbFindEarliest, &trunc);
|
|
earliest = trunc.earliestExistingPage * MULTIXACT_OFFSETS_PER_PAGE;
|
|
if (earliest < FirstMultiXactId)
|
|
earliest = FirstMultiXactId;
|
|
|
|
/* If there's nothing to remove, we can bail out early. */
|
|
if (MultiXactIdPrecedes(oldestMulti, earliest))
|
|
{
|
|
LWLockRelease(MultiXactTruncationLock);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* First, compute the safe truncation point for MultiXactMember. This is
|
|
* the starting offset of the oldest multixact.
|
|
*
|
|
* Hopefully, find_multixact_start will always work here, because we've
|
|
* already checked that it doesn't precede the earliest MultiXact on disk.
|
|
* But if it fails, don't truncate anything, and log a message.
|
|
*/
|
|
if (oldestMulti == nextMulti)
|
|
{
|
|
/* there are NO MultiXacts */
|
|
oldestOffset = nextOffset;
|
|
}
|
|
else if (!find_multixact_start(oldestMulti, &oldestOffset))
|
|
{
|
|
ereport(LOG,
|
|
(errmsg("oldest MultiXact %u not found, earliest MultiXact %u, skipping truncation",
|
|
oldestMulti, earliest)));
|
|
LWLockRelease(MultiXactTruncationLock);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Secondly compute up to where to truncate. Lookup the corresponding
|
|
* member offset for newOldestMulti for that.
|
|
*/
|
|
if (newOldestMulti == nextMulti)
|
|
{
|
|
/* there are NO MultiXacts */
|
|
newOldestOffset = nextOffset;
|
|
}
|
|
else if (!find_multixact_start(newOldestMulti, &newOldestOffset))
|
|
{
|
|
ereport(LOG,
|
|
(errmsg("cannot truncate up to MultiXact %u because it does not exist on disk, skipping truncation",
|
|
newOldestMulti)));
|
|
LWLockRelease(MultiXactTruncationLock);
|
|
return;
|
|
}
|
|
|
|
elog(DEBUG1, "performing multixact truncation: "
|
|
"offsets [%u, %u), offsets segments [%x, %x), "
|
|
"members [%u, %u), members segments [%x, %x)",
|
|
oldestMulti, newOldestMulti,
|
|
MultiXactIdToOffsetSegment(oldestMulti),
|
|
MultiXactIdToOffsetSegment(newOldestMulti),
|
|
oldestOffset, newOldestOffset,
|
|
MXOffsetToMemberSegment(oldestOffset),
|
|
MXOffsetToMemberSegment(newOldestOffset));
|
|
|
|
/*
|
|
* Do truncation, and the WAL logging of the truncation, in a critical
|
|
* section. That way offsets/members cannot get out of sync anymore, i.e.
|
|
* once consistent the newOldestMulti will always exist in members, even
|
|
* if we crashed in the wrong moment.
|
|
*/
|
|
START_CRIT_SECTION();
|
|
|
|
/*
|
|
* Prevent checkpoints from being scheduled concurrently. This is critical
|
|
* because otherwise a truncation record might not be replayed after a
|
|
* crash/basebackup, even though the state of the data directory would
|
|
* require it.
|
|
*/
|
|
Assert(!MyProc->delayChkpt);
|
|
MyProc->delayChkpt = true;
|
|
|
|
/* WAL log truncation */
|
|
WriteMTruncateXlogRec(newOldestMultiDB,
|
|
oldestMulti, newOldestMulti,
|
|
oldestOffset, newOldestOffset);
|
|
|
|
/*
|
|
* Update in-memory limits before performing the truncation, while inside
|
|
* the critical section: Have to do it before truncation, to prevent
|
|
* concurrent lookups of those values. Has to be inside the critical
|
|
* section as otherwise a future call to this function would error out,
|
|
* while looking up the oldest member in offsets, if our caller crashes
|
|
* before updating the limits.
|
|
*/
|
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
|
MultiXactState->oldestMultiXactId = newOldestMulti;
|
|
MultiXactState->oldestMultiXactDB = newOldestMultiDB;
|
|
LWLockRelease(MultiXactGenLock);
|
|
|
|
/* First truncate members */
|
|
PerformMembersTruncation(oldestOffset, newOldestOffset);
|
|
|
|
/* Then offsets */
|
|
PerformOffsetsTruncation(oldestMulti, newOldestMulti);
|
|
|
|
MyProc->delayChkpt = false;
|
|
|
|
END_CRIT_SECTION();
|
|
LWLockRelease(MultiXactTruncationLock);
|
|
}
|
|
|
|
/*
|
|
* Decide which of two MultiXactOffset page numbers is "older" for truncation
|
|
* purposes.
|
|
*
|
|
* We need to use comparison of MultiXactId here in order to do the right
|
|
* thing with wraparound. However, if we are asked about page number zero, we
|
|
* don't want to hand InvalidMultiXactId to MultiXactIdPrecedes: it'll get
|
|
* weird. So, offset both multis by FirstMultiXactId to avoid that.
|
|
* (Actually, the current implementation doesn't do anything weird with
|
|
* InvalidMultiXactId, but there's no harm in leaving this code like this.)
|
|
*/
|
|
static bool
|
|
MultiXactOffsetPagePrecedes(int page1, int page2)
|
|
{
|
|
MultiXactId multi1;
|
|
MultiXactId multi2;
|
|
|
|
multi1 = ((MultiXactId) page1) * MULTIXACT_OFFSETS_PER_PAGE;
|
|
multi1 += FirstMultiXactId;
|
|
multi2 = ((MultiXactId) page2) * MULTIXACT_OFFSETS_PER_PAGE;
|
|
multi2 += FirstMultiXactId;
|
|
|
|
return MultiXactIdPrecedes(multi1, multi2);
|
|
}
|
|
|
|
/*
|
|
* Decide which of two MultiXactMember page numbers is "older" for truncation
|
|
* purposes. There is no "invalid offset number" so use the numbers verbatim.
|
|
*/
|
|
static bool
|
|
MultiXactMemberPagePrecedes(int page1, int page2)
|
|
{
|
|
MultiXactOffset offset1;
|
|
MultiXactOffset offset2;
|
|
|
|
offset1 = ((MultiXactOffset) page1) * MULTIXACT_MEMBERS_PER_PAGE;
|
|
offset2 = ((MultiXactOffset) page2) * MULTIXACT_MEMBERS_PER_PAGE;
|
|
|
|
return MultiXactOffsetPrecedes(offset1, offset2);
|
|
}
|
|
|
|
/*
|
|
* Decide which of two MultiXactIds is earlier.
|
|
*
|
|
* XXX do we need to do something special for InvalidMultiXactId?
|
|
* (Doesn't look like it.)
|
|
*/
|
|
bool
|
|
MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2)
|
|
{
|
|
int32 diff = (int32) (multi1 - multi2);
|
|
|
|
return (diff < 0);
|
|
}
|
|
|
|
/*
|
|
* MultiXactIdPrecedesOrEquals -- is multi1 logically <= multi2?
|
|
*
|
|
* XXX do we need to do something special for InvalidMultiXactId?
|
|
* (Doesn't look like it.)
|
|
*/
|
|
bool
|
|
MultiXactIdPrecedesOrEquals(MultiXactId multi1, MultiXactId multi2)
|
|
{
|
|
int32 diff = (int32) (multi1 - multi2);
|
|
|
|
return (diff <= 0);
|
|
}
|
|
|
|
|
|
/*
|
|
* Decide which of two offsets is earlier.
|
|
*/
|
|
static bool
|
|
MultiXactOffsetPrecedes(MultiXactOffset offset1, MultiXactOffset offset2)
|
|
{
|
|
int32 diff = (int32) (offset1 - offset2);
|
|
|
|
return (diff < 0);
|
|
}
|
|
|
|
/*
|
|
* Write an xlog record reflecting the zeroing of either a MEMBERs or
|
|
* OFFSETs page (info shows which)
|
|
*/
|
|
static void
|
|
WriteMZeroPageXlogRec(int pageno, uint8 info)
|
|
{
|
|
XLogBeginInsert();
|
|
XLogRegisterData((char *) (&pageno), sizeof(int));
|
|
(void) XLogInsert(RM_MULTIXACT_ID, info);
|
|
}
|
|
|
|
/*
|
|
* Write a TRUNCATE xlog record
|
|
*
|
|
* We must flush the xlog record to disk before returning --- see notes in
|
|
* TruncateCLOG().
|
|
*/
|
|
static void
|
|
WriteMTruncateXlogRec(Oid oldestMultiDB,
|
|
MultiXactId startTruncOff, MultiXactId endTruncOff,
|
|
MultiXactOffset startTruncMemb, MultiXactOffset endTruncMemb)
|
|
{
|
|
XLogRecPtr recptr;
|
|
xl_multixact_truncate xlrec;
|
|
|
|
xlrec.oldestMultiDB = oldestMultiDB;
|
|
|
|
xlrec.startTruncOff = startTruncOff;
|
|
xlrec.endTruncOff = endTruncOff;
|
|
|
|
xlrec.startTruncMemb = startTruncMemb;
|
|
xlrec.endTruncMemb = endTruncMemb;
|
|
|
|
XLogBeginInsert();
|
|
XLogRegisterData((char *) (&xlrec), SizeOfMultiXactTruncate);
|
|
recptr = XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_TRUNCATE_ID);
|
|
XLogFlush(recptr);
|
|
}
|
|
|
|
/*
|
|
* MULTIXACT resource manager's routines
|
|
*/
|
|
void
|
|
multixact_redo(XLogReaderState *record)
|
|
{
|
|
uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
|
|
|
|
/* Backup blocks are not used in multixact records */
|
|
Assert(!XLogRecHasAnyBlockRefs(record));
|
|
|
|
if (info == XLOG_MULTIXACT_ZERO_OFF_PAGE)
|
|
{
|
|
int pageno;
|
|
int slotno;
|
|
|
|
memcpy(&pageno, XLogRecGetData(record), sizeof(int));
|
|
|
|
LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
|
|
|
|
slotno = ZeroMultiXactOffsetPage(pageno, false);
|
|
SimpleLruWritePage(MultiXactOffsetCtl, slotno);
|
|
Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
|
|
|
|
LWLockRelease(MultiXactOffsetSLRULock);
|
|
}
|
|
else if (info == XLOG_MULTIXACT_ZERO_MEM_PAGE)
|
|
{
|
|
int pageno;
|
|
int slotno;
|
|
|
|
memcpy(&pageno, XLogRecGetData(record), sizeof(int));
|
|
|
|
LWLockAcquire(MultiXactMemberSLRULock, LW_EXCLUSIVE);
|
|
|
|
slotno = ZeroMultiXactMemberPage(pageno, false);
|
|
SimpleLruWritePage(MultiXactMemberCtl, slotno);
|
|
Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
|
|
|
|
LWLockRelease(MultiXactMemberSLRULock);
|
|
}
|
|
else if (info == XLOG_MULTIXACT_CREATE_ID)
|
|
{
|
|
xl_multixact_create *xlrec =
|
|
(xl_multixact_create *) XLogRecGetData(record);
|
|
TransactionId max_xid;
|
|
int i;
|
|
|
|
/* Store the data back into the SLRU files */
|
|
RecordNewMultiXact(xlrec->mid, xlrec->moff, xlrec->nmembers,
|
|
xlrec->members);
|
|
|
|
/* Make sure nextMXact/nextOffset are beyond what this record has */
|
|
MultiXactAdvanceNextMXact(xlrec->mid + 1,
|
|
xlrec->moff + xlrec->nmembers);
|
|
|
|
/*
|
|
* Make sure nextXid is beyond any XID mentioned in the record.
|
|
* This should be unnecessary, since any XID found here ought to have
|
|
* other evidence in the XLOG, but let's be safe.
|
|
*/
|
|
max_xid = XLogRecGetXid(record);
|
|
for (i = 0; i < xlrec->nmembers; i++)
|
|
{
|
|
if (TransactionIdPrecedes(max_xid, xlrec->members[i].xid))
|
|
max_xid = xlrec->members[i].xid;
|
|
}
|
|
|
|
AdvanceNextFullTransactionIdPastXid(max_xid);
|
|
}
|
|
else if (info == XLOG_MULTIXACT_TRUNCATE_ID)
|
|
{
|
|
xl_multixact_truncate xlrec;
|
|
int pageno;
|
|
|
|
memcpy(&xlrec, XLogRecGetData(record),
|
|
SizeOfMultiXactTruncate);
|
|
|
|
elog(DEBUG1, "replaying multixact truncation: "
|
|
"offsets [%u, %u), offsets segments [%x, %x), "
|
|
"members [%u, %u), members segments [%x, %x)",
|
|
xlrec.startTruncOff, xlrec.endTruncOff,
|
|
MultiXactIdToOffsetSegment(xlrec.startTruncOff),
|
|
MultiXactIdToOffsetSegment(xlrec.endTruncOff),
|
|
xlrec.startTruncMemb, xlrec.endTruncMemb,
|
|
MXOffsetToMemberSegment(xlrec.startTruncMemb),
|
|
MXOffsetToMemberSegment(xlrec.endTruncMemb));
|
|
|
|
/* should not be required, but more than cheap enough */
|
|
LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Advance the horizon values, so they're current at the end of
|
|
* recovery.
|
|
*/
|
|
SetMultiXactIdLimit(xlrec.endTruncOff, xlrec.oldestMultiDB, false);
|
|
|
|
PerformMembersTruncation(xlrec.startTruncMemb, xlrec.endTruncMemb);
|
|
|
|
/*
|
|
* During XLOG replay, latest_page_number isn't necessarily set up
|
|
* yet; insert a suitable value to bypass the sanity test in
|
|
* SimpleLruTruncate.
|
|
*/
|
|
pageno = MultiXactIdToOffsetPage(xlrec.endTruncOff);
|
|
MultiXactOffsetCtl->shared->latest_page_number = pageno;
|
|
PerformOffsetsTruncation(xlrec.startTruncOff, xlrec.endTruncOff);
|
|
|
|
LWLockRelease(MultiXactTruncationLock);
|
|
}
|
|
else
|
|
elog(PANIC, "multixact_redo: unknown op code %u", info);
|
|
}
|
|
|
|
Datum
|
|
pg_get_multixact_members(PG_FUNCTION_ARGS)
|
|
{
|
|
typedef struct
|
|
{
|
|
MultiXactMember *members;
|
|
int nmembers;
|
|
int iter;
|
|
} mxact;
|
|
MultiXactId mxid = PG_GETARG_UINT32(0);
|
|
mxact *multi;
|
|
FuncCallContext *funccxt;
|
|
|
|
if (mxid < FirstMultiXactId)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
|
|
errmsg("invalid MultiXactId: %u", mxid)));
|
|
|
|
if (SRF_IS_FIRSTCALL())
|
|
{
|
|
MemoryContext oldcxt;
|
|
TupleDesc tupdesc;
|
|
|
|
funccxt = SRF_FIRSTCALL_INIT();
|
|
oldcxt = MemoryContextSwitchTo(funccxt->multi_call_memory_ctx);
|
|
|
|
multi = palloc(sizeof(mxact));
|
|
/* no need to allow for old values here */
|
|
multi->nmembers = GetMultiXactIdMembers(mxid, &multi->members, false,
|
|
false);
|
|
multi->iter = 0;
|
|
|
|
tupdesc = CreateTemplateTupleDesc(2);
|
|
TupleDescInitEntry(tupdesc, (AttrNumber) 1, "xid",
|
|
XIDOID, -1, 0);
|
|
TupleDescInitEntry(tupdesc, (AttrNumber) 2, "mode",
|
|
TEXTOID, -1, 0);
|
|
|
|
funccxt->attinmeta = TupleDescGetAttInMetadata(tupdesc);
|
|
funccxt->user_fctx = multi;
|
|
|
|
MemoryContextSwitchTo(oldcxt);
|
|
}
|
|
|
|
funccxt = SRF_PERCALL_SETUP();
|
|
multi = (mxact *) funccxt->user_fctx;
|
|
|
|
while (multi->iter < multi->nmembers)
|
|
{
|
|
HeapTuple tuple;
|
|
char *values[2];
|
|
|
|
values[0] = psprintf("%u", multi->members[multi->iter].xid);
|
|
values[1] = mxstatus_to_string(multi->members[multi->iter].status);
|
|
|
|
tuple = BuildTupleFromCStrings(funccxt->attinmeta, values);
|
|
|
|
multi->iter++;
|
|
pfree(values[0]);
|
|
SRF_RETURN_NEXT(funccxt, HeapTupleGetDatum(tuple));
|
|
}
|
|
|
|
SRF_RETURN_DONE(funccxt);
|
|
}
|
|
|
|
/*
|
|
* Entrypoint for sync.c to sync offsets files.
|
|
*/
|
|
int
|
|
multixactoffsetssyncfiletag(const FileTag *ftag, char *path)
|
|
{
|
|
return SlruSyncFileTag(MultiXactOffsetCtl, ftag, path);
|
|
}
|
|
|
|
/*
|
|
* Entrypoint for sync.c to sync members files.
|
|
*/
|
|
int
|
|
multixactmemberssyncfiletag(const FileTag *ftag, char *path)
|
|
{
|
|
return SlruSyncFileTag(MultiXactMemberCtl, ftag, path);
|
|
}
|