Re: [HACKERS] New wal_sync_method for Darwin? - Mailing list pgsql-patches

Attached is an updated version of your Darwin Fsync-writethrough patch.
I did much more restructuring because we do fsync in more places than
just WAL (like at checkpoints), and we should follow the WAL
write-through in those places too if that method is used for fsync of
WAL, rather than the normal fsync without the force-writethrough.

I restructured the code so now pg_fsync does writethrough or not based
on the wal setting.  My feeling is you need WAL writethrough, you need
it for other fsyncs as well.  Write-through was added in an 8.0.X
subrelease, and because it was a subrelease, the patch did a minimal
amount of code change.  This change is the restructuring that makes
sense for 8.1.

---------------------------------------------------------------------------

Chris Campbell wrote:
> Thanks, Bruce! Here's the patch (would you rather patches be attached
> files, or inline?).
>
> Some explanation. In the current code, there is no "fsync" on Windows,
> only "fsync_writethrough". But, internally, it behaves identically to
> "fsync". The only special case was for the GUC strings.
>
> The patch changes it thusly: since "fsync" and "fsync_writethrough"
> cannot be identical on Darwin, I added a new constant for
> SYNC_METHOD_FSYNC_WRITE_THROUGH (3). A GUC value of
> "fsync_writethrough" sets fsync_method to this new constant.
>
> On Windows, the fsync_writethrough case falls through to the fsync case
> (which simply runs fsync). On Darwin, the fsync_writethrough case
> executes fcntl(openLogFile, F_FULLFSYNC, 0), which does everything that
> fsync does, and then flushes the disk's write cache. The code does not
> need to call fsync directly, just fcntl.
>
> The performance of a script that executes 11,000 INSERT statements
> (outside a transaction) is pretty slow, since it requires flushing the
> disk write cache after EVERY query (transaction commit). I waited about
> 15 minutes before I just killed it. But if you do all the inserts
> inside a transaction, then I only pay the cache flush price once at
> transaction commit, and it's quite usable.
>
> I asked around on IRC, and the only place where flushing the disk cache
> is important is when syncing a WAL file. So I didn't change the
> behavior of fsync() globally for the code...just for WAL syncs.
>
> I added a new #define called HAVE_FSYNC_WRITE_THROUGH, which is defined
> only by the win32.h and darwin.h port headers. This controls the
> availability of the "fsync_writethrough" GUC setting. Thanks to the
> port headers, no configure test is needed.
>
> Thanks! Let me know what you think of the patch, and tell me what else
> I can do.
>
> - Chris
>
>

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073
Index: doc/src/sgml/runtime.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v
retrieving revision 1.319
diff -c -c -r1.319 runtime.sgml
*** doc/src/sgml/runtime.sgml    15 May 2005 00:26:18 -0000    1.319
--- doc/src/sgml/runtime.sgml    17 May 2005 22:03:49 -0000
***************
*** 1595,1601 ****
          values are
          <literal>fsync</> (call <function>fsync()</> at each commit),
          <literal>fdatasync</> (call <function>fdatasync()</> at each commit),
!         <literal>fsync_writethrough</> (call <function>_commit()</> at each commit on Windows),
          <literal>open_sync</> (write WAL files with <function>open()</> option <symbol>O_SYNC</>), and
          <literal>open_datasync</> (write WAL files with <function>open()</> option <symbol>O_DSYNC</>).
          Not all of these choices are available on all platforms.
--- 1595,1601 ----
          values are
          <literal>fsync</> (call <function>fsync()</> at each commit),
          <literal>fdatasync</> (call <function>fdatasync()</> at each commit),
!         <literal>fsync_writethrough</> (force write-through of any disk write cache),
          <literal>open_sync</> (write WAL files with <function>open()</> option <symbol>O_SYNC</>), and
          <literal>open_datasync</> (write WAL files with <function>open()</> option <symbol>O_DSYNC</>).
          Not all of these choices are available on all platforms.
Index: src/backend/access/transam/xlog.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v
retrieving revision 1.191
diff -c -c -r1.191 xlog.c
*** src/backend/access/transam/xlog.c    10 May 2005 22:27:29 -0000    1.191
--- src/backend/access/transam/xlog.c    17 May 2005 22:03:53 -0000
***************
*** 51,61 ****
   * default method.    We assume that fsync() is always available, and that
   * configure determined whether fdatasync() is.
   */
- #define SYNC_METHOD_FSYNC        0
- #define SYNC_METHOD_FDATASYNC    1
- #define SYNC_METHOD_OPEN        2        /* used for both O_SYNC and
-                                          * O_DSYNC */
-
  #if defined(O_SYNC)
  #define OPEN_SYNC_FLAG       O_SYNC
  #else
--- 51,56 ----
***************
*** 79,99 ****
  #define DEFAULT_SYNC_METHOD_STR    "open_datasync"
  #define DEFAULT_SYNC_METHOD           SYNC_METHOD_OPEN
  #define DEFAULT_SYNC_FLAGBIT       OPEN_DATASYNC_FLAG
! #else
! #if defined(HAVE_FDATASYNC)
  #define DEFAULT_SYNC_METHOD_STR   "fdatasync"
  #define DEFAULT_SYNC_METHOD          SYNC_METHOD_FDATASYNC
  #define DEFAULT_SYNC_FLAGBIT      0
! #else
! #ifndef FSYNC_IS_WRITE_THROUGH
  #define DEFAULT_SYNC_METHOD_STR   "fsync"
  #else
  #define DEFAULT_SYNC_METHOD_STR   "fsync_writethrough"
! #endif
! #define DEFAULT_SYNC_METHOD          SYNC_METHOD_FSYNC
  #define DEFAULT_SYNC_FLAGBIT      0
  #endif
- #endif


  /* User-settable parameters */
--- 74,92 ----
  #define DEFAULT_SYNC_METHOD_STR    "open_datasync"
  #define DEFAULT_SYNC_METHOD           SYNC_METHOD_OPEN
  #define DEFAULT_SYNC_FLAGBIT       OPEN_DATASYNC_FLAG
! #elif defined(HAVE_FDATASYNC)
  #define DEFAULT_SYNC_METHOD_STR   "fdatasync"
  #define DEFAULT_SYNC_METHOD          SYNC_METHOD_FDATASYNC
  #define DEFAULT_SYNC_FLAGBIT      0
! #elif !defined(HAVE_FSYNC_WRITETHROUGH_ONLY)
  #define DEFAULT_SYNC_METHOD_STR   "fsync"
+ #define DEFAULT_SYNC_METHOD          SYNC_METHOD_FSYNC
+ #define DEFAULT_SYNC_FLAGBIT      0
  #else
  #define DEFAULT_SYNC_METHOD_STR   "fsync_writethrough"
! #define DEFAULT_SYNC_METHOD          SYNC_METHOD_FSYNC_WRITETHROUGH
  #define DEFAULT_SYNC_FLAGBIT      0
  #endif


  /* User-settable parameters */
***************
*** 122,128 ****


  /* these are derived from XLOG_sync_method by assign_xlog_sync_method */
! static int    sync_method = DEFAULT_SYNC_METHOD;
  static int    open_sync_bit = DEFAULT_SYNC_FLAGBIT;

  #define XLOG_SYNC_BIT  (enableFsync ? open_sync_bit : 0)
--- 115,121 ----


  /* these are derived from XLOG_sync_method by assign_xlog_sync_method */
! int    sync_method = DEFAULT_SYNC_METHOD;
  static int    open_sync_bit = DEFAULT_SYNC_FLAGBIT;

  #define XLOG_SYNC_BIT  (enableFsync ? open_sync_bit : 0)
***************
*** 5249,5264 ****
      int            new_sync_method;
      int            new_sync_bit;

- #ifndef FSYNC_IS_WRITE_THROUGH
      if (pg_strcasecmp(method, "fsync") == 0)
- #else
-     /* Win32 fsync() == _commit(), which writes through a write cache */
-     if (pg_strcasecmp(method, "fsync_writethrough") == 0)
- #endif
      {
          new_sync_method = SYNC_METHOD_FSYNC;
          new_sync_bit = 0;
      }
  #ifdef HAVE_FDATASYNC
      else if (pg_strcasecmp(method, "fdatasync") == 0)
      {
--- 5242,5259 ----
      int            new_sync_method;
      int            new_sync_bit;

      if (pg_strcasecmp(method, "fsync") == 0)
      {
          new_sync_method = SYNC_METHOD_FSYNC;
          new_sync_bit = 0;
      }
+ #ifdef HAVE_FSYNC_WRITETHROUGH
+     else if (pg_strcasecmp(method, "fsync_writethrough") == 0)
+     {
+         new_sync_method = SYNC_METHOD_FSYNC_WRITETHROUGH;
+         new_sync_bit = 0;
+     }
+ #endif
  #ifdef HAVE_FDATASYNC
      else if (pg_strcasecmp(method, "fdatasync") == 0)
      {
***************
*** 5328,5339 ****
      switch (sync_method)
      {
          case SYNC_METHOD_FSYNC:
!             if (pg_fsync(openLogFile) != 0)
                  ereport(PANIC,
                          (errcode_for_file_access(),
                      errmsg("could not fsync log file %u, segment %u: %m",
                             openLogId, openLogSeg)));
              break;
  #ifdef HAVE_FDATASYNC
          case SYNC_METHOD_FDATASYNC:
              if (pg_fdatasync(openLogFile) != 0)
--- 5323,5343 ----
      switch (sync_method)
      {
          case SYNC_METHOD_FSYNC:
!             if (pg_fsync_no_writethrough(openLogFile) != 0)
                  ereport(PANIC,
                          (errcode_for_file_access(),
                      errmsg("could not fsync log file %u, segment %u: %m",
                             openLogId, openLogSeg)));
              break;
+ #ifdef HAVE_FSYNC_WRITETHROUGH
+         case SYNC_METHOD_FSYNC_WRITETHROUGH:
+             if (pg_fsync_writethrough(openLogFile) != 0)
+                 ereport(PANIC,
+                         (errcode_for_file_access(),
+                     errmsg("could not fsync write-through log file %u, segment %u: %m",
+                            openLogId, openLogSeg)));
+             break;
+ #endif
  #ifdef HAVE_FDATASYNC
          case SYNC_METHOD_FDATASYNC:
              if (pg_fdatasync(openLogFile) != 0)
Index: src/backend/storage/file/fd.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/storage/file/fd.c,v
retrieving revision 1.115
diff -c -c -r1.115 fd.c
*** src/backend/storage/file/fd.c    31 Dec 2004 22:00:51 -0000    1.115
--- src/backend/storage/file/fd.c    17 May 2005 22:03:54 -0000
***************
*** 232,242 ****


  /*
!  * pg_fsync --- same as fsync except does nothing if enableFsync is off
   */
  int
  pg_fsync(int fd)
  {
      if (enableFsync)
          return fsync(fd);
      else
--- 232,258 ----


  /*
!  * pg_fsync --- do fsync with or without writethrough
   */
  int
  pg_fsync(int fd)
  {
+ #ifndef HAVE_FSYNC_WRITETHROUGH_ONLY
+     if (sync_method != SYNC_METHOD_FSYNC_WRITETHROUGH)
+         return pg_fsync_no_writethrough(fd);
+     else
+ #endif
+         return pg_fsync_writethrough(fd);
+ }
+
+
+ /*
+  * pg_fsync_no_writethrough --- same as fsync except does nothing if
+  *    enableFsync is off
+  */
+ int
+ pg_fsync_no_writethrough(int fd)
+ {
      if (enableFsync)
          return fsync(fd);
      else
***************
*** 244,249 ****
--- 260,283 ----
  }

  /*
+  * pg_fsync_writethrough
+  */
+ int
+ pg_fsync_writethrough(int fd)
+ {
+     if (enableFsync)
+ #ifdef WIN32
+         return _commit(fd);
+ #elif defined(__darwin__)
+         return (fcntl(fd, F_FULLFSYNC, 0) == -1) ? -1 : 0;
+ #else
+         return -1;
+ #endif
+     else
+         return 0;
+ }
+
+ /*
   * pg_fdatasync --- same as fdatasync except does nothing if enableFsync is off
   *
   * Not all platforms have fdatasync; treat as fsync if not available.
Index: src/include/access/xlog.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/access/xlog.h,v
retrieving revision 1.60
diff -c -c -r1.60 xlog.h
*** src/include/access/xlog.h    28 Apr 2005 21:47:17 -0000    1.60
--- src/include/access/xlog.h    17 May 2005 22:03:56 -0000
***************
*** 75,80 ****
--- 75,87 ----
   */
  #define XLOG_NO_TRAN            XLR_INFO_MASK

+ /* Sync methods */
+ #define SYNC_METHOD_FSYNC        0
+ #define SYNC_METHOD_FDATASYNC    1
+ #define SYNC_METHOD_OPEN        2            /* for O_SYNC and O_DSYNC */
+ #define SYNC_METHOD_FSYNC_WRITETHROUGH    3
+ extern int    sync_method;
+
  /*
   * List of these structs is used to pass data to XLogInsert().
   *
Index: src/include/port/darwin.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/port/darwin.h,v
retrieving revision 1.6
diff -c -c -r1.6 darwin.h
*** src/include/port/darwin.h    23 Dec 2003 03:31:30 -0000    1.6
--- src/include/port/darwin.h    17 May 2005 22:03:57 -0000
***************
*** 1 ****
--- 1,4 ----
  #define __darwin__    1
+
+ #define HAVE_FSYNC_WRITETHROUGH
+
Index: src/include/port/win32.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/port/win32.h,v
retrieving revision 1.44
diff -c -c -r1.44 win32.h
*** src/include/port/win32.h    24 Mar 2005 04:36:19 -0000    1.44
--- src/include/port/win32.h    17 May 2005 22:03:57 -0000
***************
*** 16,23 ****
  #define mkdir(a,b)    mkdir(a)


! #define fsync(a)    _commit(a)
! #define FSYNC_IS_WRITE_THROUGH
  #define ftruncate(a,b)    chsize(a,b)

  #define USES_WINSOCK
--- 16,23 ----
  #define mkdir(a,b)    mkdir(a)


! #define HAVE_FSYNC_WRITETHROUGH
! #define HAVE_FSYNC_WRITETHROUGH_ONLY
  #define ftruncate(a,b)    chsize(a,b)

  #define USES_WINSOCK
Index: src/include/storage/fd.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/storage/fd.h,v
retrieving revision 1.50
diff -c -c -r1.50 fd.h
*** src/include/storage/fd.h    31 Dec 2004 22:03:42 -0000    1.50
--- src/include/storage/fd.h    17 May 2005 22:03:57 -0000
***************
*** 89,94 ****
--- 89,96 ----
                                SubTransactionId parentSubid);
  extern void RemovePgTempFiles(void);
  extern int    pg_fsync(int fd);
+ extern int    pg_fsync_no_writethrough(int fd);
+ extern int    pg_fsync_writethrough(int fd);
  extern int    pg_fdatasync(int fd);

  /* Filename components for OpenTemporaryFile */