Re: [HACKERS] no universally correct setting for fsync

Folks,

This is what I have to replace the current fsync entry in config.sgml.

I believe that the note about needing fsync for Warm Standby to work
correctly is true, but could someone verify it?

=========================

<varlistentry id="guc-fsync" xreflabel="fsync">
<indexterm>
<primary><varname>fsync</> configuration parameter</primary>
</indexterm>
<term><varname>fsync</varname> (<type>boolean</type>)</term>
<listitem>
<para>
If this parameter is on, the <productname>PostgreSQL</> server
will try to make sure that updates are physically written to
disk, by issuing <function>fsync()</> system calls or various
equivalent methods (see <xref linkend="guc-wal-sync-method">).
This ensures that the database cluster can recover to a
consistent state after an operating system or hardware crash.
</para>

<para>
While turning off <varname>fsync</varname> is often a performance
benefit, this can result in unrecoverable data corruption in the
event
of an unexpected shutdown. Thus it is only advisable to turn off
<varname>fsync</varname> if you can easily recreate
your entire database from external data. <varname>fsync</varname>
must be on for WAL archiving to work correctly
(see <xref linkend="continuous-archiving">).
<para>

<para>
In many situations, turning off <xref
linkend="guc-synchronous-commit">
for noncritical transactions can provide much of the potential
performance benefit of turning off <varname>fsync</varname>, without
the attendant risks of data corruption.
</para>

<para>
<varname>fsync</varname> can only be set in the
<filename>postgresql.conf</>
file or on the server command line.
If you turn this parameter off, also consider turning off
<xref linkend="guc-full-page-writes">.
</para>
</listitem>
</varlistentry>

--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com