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Force default wal_sync_method to be fdatasync on Linux.

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Recent versions of the Linux system header files cause xlogdefs.h to
believe that open_datasync should be the default sync method, whereas
formerly fdatasync was the default on Linux.  open_datasync is a bad
choice, first because it doesn't actually outperform fdatasync (in fact
the reverse), and second because we try to use O_DIRECT with it, causing
failures on certain filesystems (e.g., ext4 with data=journal option).
This part of the patch is largely per a proposal from Marti Raudsepp.
More extensive changes are likely to follow in HEAD, but this is as much
change as we want to back-patch.

Also clean up confusing code and incorrect documentation surrounding the
fsync_writethrough option.  Those changes shouldn't result in any actual
behavioral change, but I chose to back-patch them anyway to keep the
branches looking similar in this area.

In 9.0 and HEAD, also do some copy-editing on the WAL Reliability
documentation section.

Back-patch to all supported branches, since any of them might get used
on modern Linux versions.
This commit is contained in:
Tom Lane
2010-12-08 20:01:09 -05:00
parent e620ee35b2
commit 576477e73c
7 changed files with 78 additions and 63 deletions
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9
src/backend/storage/file/fd.c
View File

@ -260,12 +260,13 @@ static bool looks_like_temp_rel_name(const char *name);
int
pg_fsync(int fd)
{
#ifndef HAVE_FSYNC_WRITETHROUGH_ONLY
if (sync_method != SYNC_METHOD_FSYNC_WRITETHROUGH)
return pg_fsync_no_writethrough(fd);
/* #if is to skip the sync_method test if there's no need for it */
#if defined(HAVE_FSYNC_WRITETHROUGH) && !defined(FSYNC_WRITETHROUGH_IS_FSYNC)
if (sync_method == SYNC_METHOD_FSYNC_WRITETHROUGH)
return pg_fsync_writethrough(fd);
else
#endif
return pg_fsync_writethrough(fd);
return pg_fsync_no_writethrough(fd);
}