Re: [HACKERS] New wal_sync_method for Darwin?

Applied.

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

Bruce Momjian wrote:
>
> 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(at)candle(dot)pha(dot)pa(dot)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 */

>
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--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073