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Support syncing WAL log to disk using either fsync(), fdatasync(),

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O_SYNC, or O_DSYNC (as available on a given platform).  Add GUC parameter
to control sync method.
Also, add defense to XLogWrite to prevent it from going nuts if passed
a target write position that's past the end of the buffers so far filled
by XLogInsert.
This commit is contained in:
Tom Lane
2001-03-16 05:44:33 +00:00
parent 4eb5e27a28
commit 9d645fd84c
6 changed files with 287 additions and 62 deletions
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23
doc/src/sgml/runtime.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.56 2001/03/13 01:17:05 tgl Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.57 2001/03/16 05:44:33 tgl Exp $
-->
<Chapter Id="runtime">
@ -1224,8 +1224,8 @@ env PGOPTIONS='-c geqo=off' psql
<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 buffers in shared memory for WAL log.
This option can only be set at server start.
</para>
</listitem>
</varlistentry>
@ -1250,6 +1250,23 @@ env PGOPTIONS='-c geqo=off' psql
</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>

29
doc/src/sgml/wal.sgml
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@ -1,4 +1,4 @@
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v 1.4 2001/03/13 01:17:05 tgl Exp $ -->
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v 1.5 2001/03/16 05:44:33 tgl Exp $ -->
<chapter id="wal">
<title>Write-Ahead Logging (<acronym>WAL</acronym>)</title>
@ -281,15 +281,6 @@
<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
@ -304,6 +295,24 @@
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>