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, 32 insertions, 25 deletions

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index b8bedca04a4..a2ce617c8ce 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -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",
@@ -2101,19 +2103,6 @@ TrimMultiXact(void)
 }
 
 /*
- * 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
  */
 void
@@ -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);
+}