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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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6
src/include/access/xlogdefs.h
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@@ -123,12 +123,12 @@ typedef uint32 TimeLineID;
#endif
#endif
#if defined(OPEN_DATASYNC_FLAG)
#if defined(PLATFORM_DEFAULT_SYNC_METHOD)
#define DEFAULT_SYNC_METHOD PLATFORM_DEFAULT_SYNC_METHOD
#elif defined(OPEN_DATASYNC_FLAG)
#define DEFAULT_SYNC_METHOD SYNC_METHOD_OPEN_DSYNC
#elif defined(HAVE_FDATASYNC)
#define DEFAULT_SYNC_METHOD SYNC_METHOD_FDATASYNC
#elif defined(HAVE_FSYNC_WRITETHROUGH_ONLY)
#define DEFAULT_SYNC_METHOD SYNC_METHOD_FSYNC_WRITETHROUGH
#else
#define DEFAULT_SYNC_METHOD SYNC_METHOD_FSYNC
#endif