Re-enable the old code in xlog.c that tried to use posix_fadvise(), so that

we can get some buildfarm feedback about whether that function is still
problematic.  (Note that the planned async-preread patch will not really
prove anything one way or the other in buildfarm testing, since it will
be inactive with default GUC settings.)

configure

@@ -16238,7 +16238,8 @@ fi
 
 
 
-for ac_func in cbrt dlopen fcvt fdatasync getpeereid getpeerucred getrlimit memmove poll pstat readlink setproctitle setsid sigprocmask symlink sysconf towlower utime utimes waitpid wcstombs
+
+for ac_func in cbrt dlopen fcvt fdatasync getpeereid getpeerucred getrlimit memmove poll posix_fadvise pstat readlink setproctitle setsid sigprocmask symlink sysconf towlower utime utimes waitpid wcstombs
 do
 as_ac_var=`echo "ac_cv_func_$ac_func" | $as_tr_sh`
 { echo "$as_me:$LINENO: checking for $ac_func" >&5

configure.in

 dnl Process this file with autoconf to produce a configure script.
-dnl $PostgreSQL: pgsql/configure.in,v 1.584 2009/01/07 10:38:44 petere Exp $
+dnl $PostgreSQL: pgsql/configure.in,v 1.585 2009/01/11 18:02:17 tgl Exp $
 dnl
 dnl Developers, please strive to achieve this order:
 dnl
@@ -1137,7 +1137,7 @@ PGAC_VAR_INT_TIMEZONE
 AC_FUNC_ACCEPT_ARGTYPES
 PGAC_FUNC_GETTIMEOFDAY_1ARG
 
-AC_CHECK_FUNCS([cbrt dlopen fcvt fdatasync getpeereid getpeerucred getrlimit memmove poll pstat readlink setproctitle setsid sigprocmask symlink sysconf towlower utime utimes waitpid wcstombs])
+AC_CHECK_FUNCS([cbrt dlopen fcvt fdatasync getpeereid getpeerucred getrlimit memmove poll posix_fadvise pstat readlink setproctitle setsid sigprocmask symlink sysconf towlower utime utimes waitpid wcstombs])
 
 AC_CHECK_DECLS(fdatasync, [], [], [#include <unistd.h>])
 AC_CHECK_DECLS(posix_fadvise, [], [], [#include <fcntl.h>])

src/backend/access/transam/xlog.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.326 2009/01/01 17:23:36 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.327 2009/01/11 18:02:17 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -17,6 +17,7 @@
 #include <ctype.h>
 #include <signal.h>
 #include <time.h>
+#include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/time.h>
 #include <sys/wait.h>
@@ -2435,30 +2436,18 @@ XLogFileClose(void)
 {
 	Assert(openLogFile >= 0);
 
-	/*
-	 * posix_fadvise is problematic on many platforms: on older x86 Linux it
-	 * just dumps core, and there are reports of problems on PPC platforms as
-	 * well.  The following is therefore disabled for the time being. We could
-	 * consider some kind of configure test to see if it's safe to use, but
-	 * since we lack hard evidence that there's any useful performance gain to
-	 * be had, spending time on that seems unprofitable for now.
-	 */
-#ifdef NOT_USED
-
 	/*
 	 * WAL segment files will not be re-read in normal operation, so we advise
-	 * 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.
-	 *
-	 * While O_DIRECT works for O_SYNC, posix_fadvise() works for fsync() and
-	 * O_SYNC, and some platforms only have posix_fadvise().
-	 */
-#if defined(HAVE_DECL_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
-	if (!XLogArchivingActive())
-		posix_fadvise(openLogFile, 0, 0, POSIX_FADV_DONTNEED);
+	 * 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.
+	 */
+#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
+	if (!XLogArchivingActive() &&
+		(get_sync_bit(sync_method) & PG_O_DIRECT) == 0)
+		(void) posix_fadvise(openLogFile, 0, 0, POSIX_FADV_DONTNEED);
 #endif
-#endif   /* NOT_USED */
 
 	if (close(openLogFile))
 		ereport(PANIC,

src/include/pg_config.h.in

@@ -336,6 +336,9 @@
 /* Define to 1 if you have the <poll.h> header file. */
 #undef HAVE_POLL_H
 
+/* Define to 1 if you have the `posix_fadvise' function. */
+#undef HAVE_POSIX_FADVISE
+
 /* Define to 1 if you have the POSIX signal interface. */
 #undef HAVE_POSIX_SIGNALS
 

src/include/pg_config_manual.h

@@ -6,7 +6,7 @@
  * for developers.	If you edit any of these, be sure to do a *full*
  * rebuild (and an initdb if noted).
  *
- * $PostgreSQL: pgsql/src/include/pg_config_manual.h,v 1.35 2008/07/12 02:28:43 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/pg_config_manual.h,v 1.36 2009/01/11 18:02:17 tgl Exp $
  *------------------------------------------------------------------------
  */
 
@@ -112,7 +112,7 @@
 #define ALIGNOF_BUFFER	32
 
 /*
- * Disable UNIX sockets for those operating system.
+ * Disable UNIX sockets for certain operating systems.
  */
 #if defined(WIN32)
 #undef HAVE_UNIX_SOCKETS
@@ -125,6 +125,16 @@
 #define HAVE_WORKING_LINK 1
 #endif
 
+/*
+ * USE_POSIX_FADVISE controls whether Postgres will attempt to use the
+ * posix_fadvise() kernel call.  Usually the automatic configure tests are
+ * sufficient, but some older Linux distributions had broken versions of
+ * posix_fadvise().  If necessary you can remove the #define here.
+ */
+#if HAVE_DECL_POSIX_FADVISE && defined(HAVE_POSIX_FADVISE)
+#define USE_POSIX_FADVISE
+#endif
+
 /*
  * This is the default directory in which AF_UNIX socket files are
  * placed.	Caution: changing this risks breaking your existing client