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Try to avoid running with a full fsync request queue.

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When we need to insert a new entry and the queue is full, compact the
entire queue in the hopes of making room for the new entry.  Doing this
on every insertion might worsen contention on BgWriterCommLock, but
when the queue it's full, it's far better than allowing the backend to
perform its own fsync, per testing by Greg Smith as reported in
http://archives.postgresql.org/pgsql-hackers/2011-01/msg02665.php

Original idea from Greg Smith.  Patch by me.  Review by Chris Browne
and Greg Smith
This commit is contained in:
Robert Haas
2011-01-29 08:08:41 -05:00
parent b2826ad52d
commit 7f242d880b
2 changed files with 131 additions and 11 deletions
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8
src/backend/storage/smgr/md.c
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@@ -34,7 +34,13 @@
/* interval for calling AbsorbFsyncRequests in mdsync */
#define FSYNCS_PER_ABSORB 10
/* special values for the segno arg to RememberFsyncRequest */
/*
* Special values for the segno arg to RememberFsyncRequest.
*
* Note that CompactBgwriterRequestQueue assumes that it's OK to remove an
* fsync request from the queue if an identical, subsequent request is found.
* See comments there before making changes here.
*/
#define FORGET_RELATION_FSYNC (InvalidBlockNumber)
#define FORGET_DATABASE_FSYNC (InvalidBlockNumber-1)
#define UNLINK_RELATION_REQUEST (InvalidBlockNumber-2)