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Defer flushing of SLRU files.

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Previously, we called fsync() after writing out individual pg_xact,
pg_multixact and pg_commit_ts pages due to cache pressure, leading to
regular I/O stalls in user backends and recovery.  Collapse requests for
the same file into a single system call as part of the next checkpoint,
as we already did for relation files, using the infrastructure developed
by commit 3eb77eba.  This can cause a significant improvement to
recovery performance, especially when it's otherwise CPU-bound.

Hoist ProcessSyncRequests() up into CheckPointGuts() to make it clearer
that it applies to all the SLRU mini-buffer-pools as well as the main
buffer pool.  Rearrange things so that data collected in CheckpointStats
includes SLRU activity.

Also remove the Shutdown{CLOG,CommitTS,SUBTRANS,MultiXact}() functions,
because they were redundant after the shutdown checkpoint that
immediately precedes them.  (I'm not sure if they were ever needed, but
they aren't now.)

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> (parts)
Tested-by: Jakub Wartak <Jakub.Wartak@tomtom.com>
Discussion: https://postgr.es/m/CA+hUKGLJ=84YT+NvhkEEDAuUtVHMfQ9i-N7k_o50JmQ6Rpj_OQ@mail.gmail.com
This commit is contained in:
Thomas Munro
2020-09-25 18:49:43 +12:00
parent ca7f8e2b86
commit dee663f784
16 changed files with 255 additions and 175 deletions
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57
src/backend/access/transam/multixact.c
View File

@@ -1831,11 +1831,13 @@ MultiXactShmemInit(void)
SimpleLruInit(MultiXactOffsetCtl,
"MultiXactOffset", NUM_MULTIXACTOFFSET_BUFFERS, 0,
MultiXactOffsetSLRULock, "pg_multixact/offsets",
LWTRANCHE_MULTIXACTOFFSET_BUFFER);
LWTRANCHE_MULTIXACTOFFSET_BUFFER,
SYNC_HANDLER_MULTIXACT_OFFSET);
SimpleLruInit(MultiXactMemberCtl,
"MultiXactMember", NUM_MULTIXACTMEMBER_BUFFERS, 0,
MultiXactMemberSLRULock, "pg_multixact/members",
LWTRANCHE_MULTIXACTMEMBER_BUFFER);
LWTRANCHE_MULTIXACTMEMBER_BUFFER,
SYNC_HANDLER_MULTIXACT_MEMBER);
/* Initialize our shared state struct */
MultiXactState = ShmemInitStruct("Shared MultiXact State",
@@ -2100,19 +2102,6 @@ TrimMultiXact(void)
SetMultiXactIdLimit(oldestMXact, oldestMXactDB, true);
}
/*
* This must be called ONCE during postmaster or standalone-backend shutdown
*/
void
ShutdownMultiXact(void)
{
/* Flush dirty MultiXact pages to disk */
TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(false);
SimpleLruFlush(MultiXactOffsetCtl, false);
SimpleLruFlush(MultiXactMemberCtl, false);
TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_DONE(false);
}
/*
* Get the MultiXact data to save in a checkpoint record
*/
@@ -2143,9 +2132,13 @@ CheckPointMultiXact(void)
{
TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(true);
/* Flush dirty MultiXact pages to disk */
SimpleLruFlush(MultiXactOffsetCtl, true);
SimpleLruFlush(MultiXactMemberCtl, 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);
}
@@ -2728,14 +2721,10 @@ find_multixact_start(MultiXactId multi, MultiXactOffset *result)
entryno = MultiXactIdToOffsetEntry(multi);
/*
* Flush out dirty data, so PhysicalPageExists can work correctly.
* SimpleLruFlush() is a pretty big hammer for that. Alternatively we
* could add an in-memory version of page exists, but find_multixact_start
* is called infrequently, and it doesn't seem bad to flush buffers to
* disk before truncation.
* Write out dirty data, so PhysicalPageExists can work correctly.
*/
SimpleLruFlush(MultiXactOffsetCtl, true);
SimpleLruFlush(MultiXactMemberCtl, true);
SimpleLruWriteAll(MultiXactOffsetCtl, true);
SimpleLruWriteAll(MultiXactMemberCtl, true);
if (!SimpleLruDoesPhysicalPageExist(MultiXactOffsetCtl, pageno))
return false;
@@ -3386,3 +3375,21 @@ pg_get_multixact_members(PG_FUNCTION_ARGS)
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);
}