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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 20:01:33 -05:00
parent 0ae63a4fb2
commit 6b2c0eab1f
6 changed files with 36 additions and 19 deletions
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8
doc/src/sgml/config.sgml
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@ -1347,12 +1347,12 @@ SET ENABLE_SEQSCAN TO OFF;
</listitem>
<listitem>
<para>
<literal>fsync_writethrough</> (call <function>fsync()</> at each commit, forcing write-through of any disk write cache)
<literal>fsync</> (call <function>fsync()</> at each commit)
</para>
</listitem>
<listitem>
<para>
<literal>fsync</> (call <function>fsync()</> at each commit)
<literal>fsync_writethrough</> (call <function>fsync()</> at each commit, forcing write-through of any disk write cache)
</para>
</listitem>
<listitem>
@ -1363,7 +1363,9 @@ SET ENABLE_SEQSCAN TO OFF;
</itemizedlist>
<para>
Not all of these choices are available on all platforms.
The default is the first method in the above list that is supported.
The default is the first method in the above list that is supported
by the platform, except that <literal>fdatasync</> is the default on
Linux.
This option can be set at server start or in the
<filename>postgresql.conf</filename> file.
</para>