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Create a new dedicated Postgres process, "wal writer", which exists to write

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and fsync WAL at convenient intervals.  For the moment it just tries to
offload this work from backends, but soon it will be responsible for
guaranteeing a maximum delay before asynchronously-committed transactions
will be flushed to disk.

This is a portion of Simon Riggs' async-commit patch, committed to CVS
separately because a background WAL writer seems like it might be a good idea
independently of the async-commit feature.  I rebased walwriter.c on
bgwriter.c because it seemed like a more appropriate way of handling signals;
while the startup/shutdown logic in postmaster.c is more like autovac because
we want walwriter to quit before we start the shutdown checkpoint.
This commit is contained in:
Tom Lane
2007-07-24 04:54:09 +00:00
parent 53d2951be7
commit ad4295728e
11 changed files with 547 additions and 70 deletions
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28
doc/src/sgml/config.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.132 2007/07/24 01:53:55 alvherre Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.133 2007/07/24 04:54:08 tgl Exp $ -->
<chapter Id="runtime-config">
<title>Server Configuration</title>
@ -1413,7 +1413,7 @@ SET ENABLE_SEQSCAN TO OFF;
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-wal-buffers" xreflabel="wal_buffers">
<term><varname>wal_buffers</varname> (<type>integer</type>)</term>
<indexterm>
@ -1438,7 +1438,27 @@ SET ENABLE_SEQSCAN TO OFF;
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-wal-writer-delay" xreflabel="wal_writer_delay">
<term><varname>wal_writer_delay</varname> (<type>integer</type>)</term>
<indexterm>
<primary><varname>wal_writer_delay</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
Specifies the delay between activity rounds for the WAL writer.
In each round the writer will flush WAL to disk. It then sleeps for
<varname>wal_writer_delay</> milliseconds, and repeats. The default
value is 200 milliseconds (<literal>200ms</>). Note that on many
systems, the effective resolution of sleep delays is 10 milliseconds;
setting <varname>wal_writer_delay</> to a value that is not a multiple
of 10 might have the same results as setting it to the next higher
multiple of 10. This parameter can only be set in the
<filename>postgresql.conf</> file or on the server command line.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-commit-delay" xreflabel="commit_delay">
<term><varname>commit_delay</varname> (<type>integer</type>)</term>
<indexterm>
@ -1521,7 +1541,7 @@ SET ENABLE_SEQSCAN TO OFF;
</indexterm>
<listitem>
<para>
Specifies the target length of checkpoints, as a fraction of
Specifies the target length of checkpoints, as a fraction of
the checkpoint interval. The default is 0.5.
This parameter can only be set in the <filename>postgresql.conf</>