[CF 5894] v02 - Don't keep closed WAL segment in page cache after replay

This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/5894

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/CAO6_Xqpx1ey8DPRub7fq4_-rtL=gygoSDHv4iLw5S3gG7=k1dw@mail.gmail.com
Author(s): Anthonin Bonnefoy

Author: Commitfest Bot

src/backend/access/transam/xlogrecovery.c

@@ -50,13 +50,15 @@
 #include "pgstat.h"
 #include "postmaster/bgwriter.h"
 #include "postmaster/startup.h"
+#include "postmaster/walsummarizer.h"
 #include "replication/slot.h"
 #include "replication/slotsync.h"
 #include "replication/walreceiver.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
 #include "storage/latch.h"
 #include "storage/pmsignal.h"
+#include "storage/proc.h"
 #include "storage/procarray.h"
 #include "storage/spin.h"
 #include "utils/datetime.h"
@@ -3358,6 +3360,24 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 			}
 		}
 
+		/*
+		 * Once replayed, WAL segment files may be re-read in several cases:
+		 * archive_mode is set to always, summarize_wal is enabled or the
+		 * standby acts as a walsender for either logical or physical
+		 * replication. Outside of those conditions, the WAL segment files
+		 * shouldn't be re-read and we can signal the kernel to release any
+		 * cached pages.
+		 */
+#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
+		{
+			int			nfree;
+
+			if (XLogArchiveMode != ARCHIVE_MODE_ALWAYS &&
+				!summarize_wal &&
+				(max_wal_senders == 0 || HaveNFreeProcs(max_wal_senders, &nfree, PROC_FREE_WALSENDER)))
+				(void) posix_fadvise(readFile, 0, 0, POSIX_FADV_DONTNEED);
+		}
+#endif
 		close(readFile);
 		readFile = -1;
 		readSource = XLOG_FROM_ANY;

src/backend/storage/lmgr/proc.c

@@ -784,17 +784,36 @@ GetStartupBufferPinWaitBufId(void)
  * Note: this is designed on the assumption that N will generally be small.
  */
 bool
-HaveNFreeProcs(int n, int *nfree)
+HaveNFreeProcs(int n, int *nfree, ProcFreeList proc_free_list)
 {
 	dlist_iter	iter;
+	dlist_head *free_list;
 
 	Assert(n > 0);
 	Assert(nfree);
 
+	switch (proc_free_list)
+	{
+		case PROC_FREE_PROCS:
+			free_list = &ProcGlobal->freeProcs;
+			break;
+		case PROC_FREE_AUTOVAC:
+			free_list = &ProcGlobal->autovacFreeProcs;
+			break;
+		case PROC_FREE_BGWORKER:
+			free_list = &ProcGlobal->bgworkerFreeProcs;
+			break;
+		case PROC_FREE_WALSENDER:
+			free_list = &ProcGlobal->walsenderFreeProcs;
+			break;
+		default:
+			elog(ERROR, "invalid free list: %d", (int) proc_free_list);
+	}
+
 	SpinLockAcquire(ProcStructLock);
 
 	*nfree = 0;
-	dlist_foreach(iter, &ProcGlobal->freeProcs)
+	dlist_foreach(iter, free_list)
 	{
 		(*nfree)++;
 		if (*nfree == n)

src/backend/utils/init/postinit.c

@@ -931,7 +931,7 @@ InitPostgres(const char *in_dbname, Oid dboid,
 	 */
 	if (AmRegularBackendProcess() && !am_superuser &&
 		(SuperuserReservedConnections + ReservedConnections) > 0 &&
-		!HaveNFreeProcs(SuperuserReservedConnections + ReservedConnections, &nfree))
+		!HaveNFreeProcs(SuperuserReservedConnections + ReservedConnections, &nfree, PROC_FREE_PROCS))
 	{
 		if (nfree < SuperuserReservedConnections)
 			ereport(FATAL,

src/include/storage/proc.h

@@ -149,6 +149,14 @@ typedef enum
 	PROC_WAIT_STATUS_ERROR,
 } ProcWaitStatus;
 
+typedef enum
+{
+	PROC_FREE_PROCS,
+	PROC_FREE_AUTOVAC,
+	PROC_FREE_BGWORKER,
+	PROC_FREE_WALSENDER,
+}			ProcFreeList;
+
 /*
  * Each backend has a PGPROC struct in shared memory.  There is also a list of
  * currently-unused PGPROC structs that will be reallocated to new backends.
@@ -497,7 +505,7 @@ extern void InitAuxiliaryProcess(void);
 extern void SetStartupBufferPinWaitBufId(int bufid);
 extern int	GetStartupBufferPinWaitBufId(void);
 
-extern bool HaveNFreeProcs(int n, int *nfree);
+extern bool HaveNFreeProcs(int n, int *nfree, ProcFreeList proc_free_list);
 extern void ProcReleaseLocks(bool isCommit);
 
 extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock,