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<Chapter Id="runtime">

<term>WAL_BUFFERS (<type>integer</type>)</term>

<listitem>

<para>

Number of disk-page buffers for WAL log. This option can only be set

at server start.

Number of disk-page buffersin shared memoryfor WAL log.

This option can only be setat server start.

</para>

</listitem>

</varlistentry>

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>WAL_SYNC_METHOD (<type>string</type>)</term>

<listitem>

<para>

Method used for forcing WAL updates out to disk. Possible

values are

<literal>FSYNC</> (call fsync() at each commit),

<literal>FDATASYNC</> (call fdatasync() at each commit),

<literal>OPEN_SYNC</> (write WAL files with open() option O_SYNC), or

<literal>OPEN_DATASYNC</> (write WAL files with open() option O_DSYNC).

Not all of these choices are available on all platforms.

This option can only be set at server start or in the

<filename>postgresql.conf</filename> file.

</para>

</listitem>

</varlistentry>

</variablelist>

</para>

</sect2>

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<chapter id="wal">

<title>Write-Ahead Logging (<acronym>WAL</acronym>)</title>

<command>CHECKPOINT</command>.

</para>

<para>

Setting the <varname>WAL_DEBUG</varname> parameter to any non-zero

value will result in each <function>LogInsert</function> and

<function>LogFlush</function> <acronym>WAL</acronym> call being

logged to standard error. At present, it makes no difference what

the non-zero value is. This option may be replaced by a more

general mechanism in the future.

</para>

<para>

The <varname>COMMIT_DELAY</varname> parameter defines for how many

microseconds the backend will sleep after writing a commit

ten milliseconds, so that any nonzero <varname>COMMIT_DELAY</varname>

setting between 1 and 10000 microseconds will have the same effect.

</para>

<para>

The <varname>WAL_SYNC_METHOD</varname> parameter determines how

Postgres will ask the kernel to force WAL updates out to disk.

All the options should be the same as far as reliability goes,

but it's quite platform-specific which one will be the fastest.

Note that this parameter is irrelevant if <varname>FSYNC</varname>

has been turned off.

</para>

<para>

Setting the <varname>WAL_DEBUG</varname> parameter to any non-zero

value will result in each <function>LogInsert</function> and

<function>LogFlush</function> <acronym>WAL</acronym> call being

logged to standard error. At present, it makes no difference what

the non-zero value is. This option may be replaced by a more

general mechanism in the future.

</para>

</sect1>

</chapter>