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Update docs to say you need fsync to make sync rep work fast.

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This commit is contained in:
Simon Riggs 2011-03-22 16:23:54 +00:00
parent 8df08c8489
commit 6e8e7cc580
1 changed files with 7 additions and 1 deletions
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8
doc/src/sgml/high-availability.sgml
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@ -947,7 +947,7 @@ synchronous_replication = on
<para> <para>
After a commit record has been written to disk on the primary the After a commit record has been written to disk on the primary the
WAL record is then sent to the standby. The standby sends reply WAL record is then sent to the standby. The standby sends reply
messages each time a new batch of WAL data is received, unless messages each time a new batch of WAL data is written to disk, unless
<varname>wal_receiver_status_interval</> is set to zero on the standby. <varname>wal_receiver_status_interval</> is set to zero on the standby.
If the standby is the first matching standby, as specified in If the standby is the first matching standby, as specified in
<varname>synchronous_standby_names</> on the primary, the reply <varname>synchronous_standby_names</> on the primary, the reply
@ -1013,6 +1013,12 @@ synchronous_replication = on
the rate of generation of WAL data. the rate of generation of WAL data.
</para> </para>
<para>
Replies are only sent when WAL is written to disk, so setting
<varname>fsync</> to <literal>off</> on the standby will significantly
reduce performance of synchronous replication and should be avoided.
</para>
</sect3> </sect3>
<sect3 id="synchronous-replication-ha"> <sect3 id="synchronous-replication-ha">