0001-Fix-use-of-posix_fadvise-in-xlog.patch

From 27958bc3ba69279719996f8495bfc63c83c8f0e1 Mon Sep 17 00:00:00 2001
From: Mark Wong <markwkm@gmail.com>
Date: Tue, 13 Oct 2009 19:29:47 -0700
Subject: [PATCH] Fix use of posix_fadvise in xlog.

Currently posix_fadvise() is called right before a log file is closed so
its benefit is hardly realized.

This fix moves posix_fadvise() into 3 new locations within
XLogFileInit().  The first case is where an existing file handle is
returned.  The next case is when a file is zeroed out.  The third case
is returning a file handle, which may be the file that was just zeroed
out.
---
 src/backend/access/transam/xlog.c |   27 ++++++++++++++++++++++-----
 1 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 622d796..1b1794e 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2255,6 +2255,12 @@ XLogNeedsFlush(XLogRecPtr record)
  * inside a critical section (eg, during checkpoint there is no reason to
  * take down the system on failure).  They will promote to PANIC if we are
  * in a critical section.
+ *
+ * WAL segment files will not be re-read in normal operation, so we advise
+ * the OS to release any cached pages.	But do not do so if WAL archiving
+ * is active, because archiver process could use the cache to read the WAL
+ * segment.  Also, don't bother with it if we are using O_DIRECT, since
+ * the kernel is presumably not caching in that case.
  */
 int
 XLogFileInit(uint32 log, uint32 seg,
@@ -2287,7 +2293,13 @@ XLogFileInit(uint32 log, uint32 seg,
 								path, log, seg)));
 		}
 		else
+		{
+#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
+			if (!XLogIsNeeded())
+				(void) posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED);
+#endif
 			return fd;
+		}
 	}
 
 	/*
@@ -2310,6 +2322,11 @@ XLogFileInit(uint32 log, uint32 seg,
 				(errcode_for_file_access(),
 				 errmsg("could not create file \"%s\": %m", tmppath)));
 
+#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
+	if (!XLogIsNeeded())
+		(void) posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED);
+#endif
+
 	/*
 	 * Zero-fill the file.	We have to do this the hard way to ensure that all
 	 * the file space has really been allocated --- on platforms that allow
@@ -2390,6 +2407,11 @@ XLogFileInit(uint32 log, uint32 seg,
 		   errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
 				  path, log, seg)));
 
+#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
+	if (!XLogIsNeeded())
+		(void) posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED);
+#endif
+
 	elog(DEBUG2, "done creating and filling new WAL file");
 
 	return fd;
@@ -2756,11 +2778,6 @@ XLogFileClose(void)
 	 * or streaming is active, because archiver and walsender process could
 	 * use the cache to read the WAL segment.
 	 */
-#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
-	if (!XLogIsNeeded())
-		(void) posix_fadvise(openLogFile, 0, 0, POSIX_FADV_DONTNEED);
-#endif
-
 	if (close(openLogFile))
 		ereport(PANIC,
 				(errcode_for_file_access(),
-- 
1.6.0.6