Defer flushing of SLRU files.

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

1 files changed, 0 insertions, 7 deletions

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index a2a963bd5b4..e549fa1d309 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -2636,14 +2636,7 @@ PrintBufferLeakWarning(Buffer buffer)
 void
 CheckPointBuffers(int flags)
 {
-	TRACE_POSTGRESQL_BUFFER_CHECKPOINT_START(flags);
-	CheckpointStats.ckpt_write_t = GetCurrentTimestamp();
 	BufferSync(flags);
-	CheckpointStats.ckpt_sync_t = GetCurrentTimestamp();
-	TRACE_POSTGRESQL_BUFFER_CHECKPOINT_SYNC_START();
-	ProcessSyncRequests();
-	CheckpointStats.ckpt_sync_end_t = GetCurrentTimestamp();
-	TRACE_POSTGRESQL_BUFFER_CHECKPOINT_DONE();
 }