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Commit269e780

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Use posix_fallocate() for new WAL files, where available.
This function is more efficient than actually writing out zeroes tothe new file, per microbenchmarks by Jon Nelson. Also, it may reducethe likelihood of WAL file fragmentation.Jon Nelson, with review by Andres Freund, Greg Smith and me.
1 parent8800d80 commit269e780

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5 files changed

+67
-37
lines changed

5 files changed

+67
-37
lines changed

‎configure

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -19695,7 +19695,8 @@ LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
1969519695

1969619696

1969719697

19698-
for ac_func in cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
19698+
19699+
for ac_func in cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate pstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
1969919700
do
1970019701
as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
1970119702
{ $as_echo "$as_me:$LINENO: checking for $ac_func" >&5

‎configure.in

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1222,7 +1222,7 @@ PGAC_FUNC_GETTIMEOFDAY_1ARG
12221222
LIBS_including_readline="$LIBS"
12231223
LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
12241224

1225-
AC_CHECK_FUNCS([cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
1225+
AC_CHECK_FUNCS([cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove pollposix_fallocatepstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
12261226

12271227
AC_REPLACE_FUNCS(fseeko)
12281228
case $host_os in

‎src/backend/access/transam/xlog.c

Lines changed: 58 additions & 35 deletions
Original file line numberDiff line numberDiff line change
@@ -2256,11 +2256,9 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
22562256
{
22572257
charpath[MAXPGPATH];
22582258
chartmppath[MAXPGPATH];
2259-
char*zbuffer;
22602259
XLogSegNoinstalled_segno;
22612260
intmax_advance;
22622261
intfd;
2263-
intnbytes;
22642262

22652263
XLogFilePath(path,ThisTimeLineID,logsegno);
22662264

@@ -2294,16 +2292,6 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
22942292

22952293
unlink(tmppath);
22962294

2297-
/*
2298-
* Allocate a buffer full of zeros. This is done before opening the file
2299-
* so that we don't leak the file descriptor if palloc fails.
2300-
*
2301-
* Note: palloc zbuffer, instead of just using a local char array, to
2302-
* ensure it is reasonably well-aligned; this may save a few cycles
2303-
* transferring data to the kernel.
2304-
*/
2305-
zbuffer= (char*)palloc0(XLOG_BLCKSZ);
2306-
23072295
/* do not use get_sync_bit() here --- want to fsync only at end of fill */
23082296
fd=BasicOpenFile(tmppath,O_RDWR |O_CREAT |O_EXCL |PG_BINARY,
23092297
S_IRUSR |S_IWUSR);
@@ -2312,38 +2300,73 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
23122300
(errcode_for_file_access(),
23132301
errmsg("could not create file \"%s\": %m",tmppath)));
23142302

2315-
/*
2316-
* Zero-fill the file.We have to do this the hard way to ensure that all
2317-
* the file space has really been allocated --- on platforms that allow
2318-
* "holes" in files, just seeking to the end doesn't allocate intermediate
2319-
* space. This way, we know that we have all the space and (after the
2320-
* fsync below) that all the indirect blocks are down on disk.Therefore,
2321-
* fdatasync(2) or O_DSYNC will be sufficient to sync future writes to the
2322-
* log file.
2323-
*/
2324-
for (nbytes=0;nbytes<XLogSegSize;nbytes+=XLOG_BLCKSZ)
2303+
#ifdefHAVE_POSIX_FALLOCATE
23252304
{
2326-
errno=0;
2327-
if ((int)write(fd,zbuffer,XLOG_BLCKSZ)!= (int)XLOG_BLCKSZ)
2328-
{
2329-
intsave_errno=errno;
2305+
errno=posix_fallocate(fd,0,XLogSegSize);
23302306

2331-
/*
2332-
* If we fail to make the file, delete it to release disk space
2333-
*/
2334-
unlink(tmppath);
2307+
if (errno)
2308+
{
2309+
interrno_saved=errno;
23352310

23362311
close(fd);
2337-
2338-
/* if write didn't set errno, assume problem is no disk space */
2339-
errno=save_errno ?save_errno :ENOSPC;
2312+
unlink(tmppath);
2313+
errno=errno_saved;
23402314

23412315
ereport(ERROR,
23422316
(errcode_for_file_access(),
2343-
errmsg("could not write to file \"%s\": %m",tmppath)));
2317+
errmsg("could not allocate space for file \"%s\" using posix_fallocate: %m",
2318+
tmppath)));
2319+
}
2320+
}
2321+
#else/* !HAVE_POSIX_FALLOCATE */
2322+
{
2323+
/*
2324+
* Allocate a buffer full of zeros. This is done before opening the
2325+
* file so that we don't leak the file descriptor if palloc fails.
2326+
*
2327+
* Note: palloc zbuffer, instead of just using a local char array, to
2328+
* ensure it is reasonably well-aligned; this may save a few cycles
2329+
* transferring data to the kernel.
2330+
*/
2331+
2332+
char*zbuffer= (char*)palloc0(XLOG_BLCKSZ);
2333+
intnbytes;
2334+
2335+
/*
2336+
* Zero-fill the file. We have to do this the hard way to ensure that
2337+
* all the file space has really been allocated --- on platforms that
2338+
* allow "holes" in files, just seeking to the end doesn't allocate
2339+
* intermediate space. This way, we know that we have all the space
2340+
* and (after the fsync below) that all the indirect blocks are down on
2341+
* disk. Therefore, fdatasync(2) or O_DSYNC will be sufficient to sync
2342+
* future writes to the log file.
2343+
*/
2344+
for (nbytes=0;nbytes<XLogSegSize;nbytes+=XLOG_BLCKSZ)
2345+
{
2346+
errno=0;
2347+
if ((int)write(fd,zbuffer,XLOG_BLCKSZ)!= (int)XLOG_BLCKSZ)
2348+
{
2349+
intsave_errno=errno;
2350+
2351+
/*
2352+
* If we fail to make the file, delete it to release disk space
2353+
*/
2354+
unlink(tmppath);
2355+
2356+
close(fd);
2357+
2358+
/* if write didn't set errno, assume no disk space */
2359+
errno=save_errno ?save_errno :ENOSPC;
2360+
2361+
ereport(ERROR,
2362+
(errcode_for_file_access(),
2363+
errmsg("could not write to file \"%s\": %m",
2364+
tmppath)));
2365+
}
23442366
}
2367+
pfree(zbuffer);
23452368
}
2346-
pfree(zbuffer);
2369+
#endif/* HAVE_POSIX_FALLOCATE */
23472370

23482371
if (pg_fsync(fd)!=0)
23492372
{

‎src/include/pg_config.h.in

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -369,6 +369,9 @@
369369
/* Define to 1 if you have the `posix_fadvise' function. */
370370
#undef HAVE_POSIX_FADVISE
371371

372+
/* Define to 1 if you have the `posix_fallocate' function. */
373+
#undef HAVE_POSIX_FALLOCATE
374+
372375
/* Define to 1 if you have the POSIX signal interface. */
373376
#undef HAVE_POSIX_SIGNALS
374377

‎src/include/pg_config.h.win32

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -276,6 +276,9 @@
276276
/* Define to 1 if you have the <poll.h> header file. */
277277
/* #undef HAVE_POLL_H */
278278

279+
/* Define to 1 if you have the `posix_fallocate' function. */
280+
/* #undef HAVE_POSIX_FALLOCATE */
281+
279282
/* Define to 1 if you have the POSIX signal interface. */
280283
/* #undef HAVE_POSIX_SIGNALS */
281284

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