Use posix_fadvise() to avoid kernel caching of WAL contents on WAL file

close.

ITAGAKI Takahiro

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index ad6767e92fb5a35b018214f21bef9d5530de616b..49e71aa12a42618959716ca453d0cd2d1ac4688c 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.237 2006/04/20 04:07:38 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.238 2006/06/15 19:15:00 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -478,6 +478,7 @@ static bool InstallXLogFileSegment(uint32 *log, uint32 *seg, char *tmppath,
                                           bool use_lock);
 static int     XLogFileOpen(uint32 log, uint32 seg);
 static int     XLogFileRead(uint32 log, uint32 seg, int emode);
+static void    XLogFileClose(void);
 static bool RestoreArchivedFile(char *path, const char *xlogfname,
                                        const char *recovername, off_t expectedSize);
 static int     PreallocXlogFiles(XLogRecPtr endptr);
@@ -1384,14 +1385,7 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
                         */
                        Assert(npages == 0);
                        if (openLogFile >= 0)
-                       {
-                               if (close(openLogFile))
-                                       ereport(PANIC,
-                                                       (errcode_for_file_access(),
-                                               errmsg("could not close log file %u, segment %u: %m",
-                                                          openLogId, openLogSeg)));
-                               openLogFile = -1;
-                       }
+                               XLogFileClose();
                        XLByteToPrevSeg(LogwrtResult.Write, openLogId, openLogSeg);
 
                        /* create/use new log file */
@@ -1567,14 +1561,7 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
                {
                        if (openLogFile >= 0 &&
                                !XLByteInPrevSeg(LogwrtResult.Write, openLogId, openLogSeg))
-                       {
-                               if (close(openLogFile))
-                                       ereport(PANIC,
-                                                       (errcode_for_file_access(),
-                                               errmsg("could not close log file %u, segment %u: %m",
-                                                          openLogId, openLogSeg)));
-                               openLogFile = -1;
-                       }
+                               XLogFileClose();
                        if (openLogFile < 0)
                        {
                                XLByteToPrevSeg(LogwrtResult.Write, openLogId, openLogSeg);
@@ -2152,6 +2139,34 @@ XLogFileRead(uint32 log, uint32 seg, int emode)
        return -1;
 }
 
+/*
+ * Close the current logfile segment for writing.
+ */
+static void
+XLogFileClose(void)
+{
+       Assert(openLogFile >= 0);
+
+#ifdef _POSIX_ADVISORY_INFO
+       /*
+        * WAL caches will not be accessed in the future, so we advise OS to
+        * free them. But we will not do so if WAL archiving is active,
+        * because archivers might use the caches 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 (!XLogArchivingActive())
+               posix_fadvise(openLogFile, 0, 0, POSIX_FADV_DONTNEED);
+#endif
+
+       if (close(openLogFile))
+               ereport(PANIC,
+                       (errcode_for_file_access(),
+                       errmsg("could not close log file %u, segment %u: %m",
+                                  openLogId, openLogSeg)));
+       openLogFile = -1;
+}
+
 /*
  * Attempt to retrieve the specified file from off-line archival storage.
  * If successful, fill "path" with its complete path (note that this will be
@@ -5609,14 +5624,7 @@ assign_xlog_sync_method(const char *method, bool doit, GucSource source)
                                                 errmsg("could not fsync log file %u, segment %u: %m",
                                                                openLogId, openLogSeg)));
                        if (open_sync_bit != new_sync_bit)
-                       {
-                               if (close(openLogFile))
-                                       ereport(PANIC,
-                                                       (errcode_for_file_access(),
-                                               errmsg("could not close log file %u, segment %u: %m",
-                                                          openLogId, openLogSeg)));
-                               openLogFile = -1;
-                       }
+                               XLogFileClose();
                }
                sync_method = new_sync_method;
                open_sync_bit = new_sync_bit;