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Commit8f9c461

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Add a paragraph explaining what restartpoints are. Mention that
wal_keep_segments does not take effect during recovery.Fujii Masao
1 parent7590ddb commit8f9c461

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2 files changed

+21
-3
lines changed

2 files changed

+21
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lines changed

‎doc/src/sgml/config.sgml

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<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.294 2010/07/08 10:20:13 mha Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.295 2010/07/16 11:20:23 heikki Exp $ -->
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<chapter Id="runtime-config">
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<title>Server Configuration</title>
@@ -1926,7 +1926,8 @@ SET ENABLE_SEQSCAN TO OFF;
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doesn't keep any extra segments for standby purposes, and the number
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of old WAL segments available to standby servers is a function of
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the location of the previous checkpoint and status of WAL
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archiving. This parameter can only be set in the
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archiving. This parameter has no effect on restartpoints.
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This parameter can only be set in the
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<filename>postgresql.conf</> file or on the server command line.
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</para>
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</listitem>

‎doc/src/sgml/wal.sgml

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<!-- $PostgreSQL: pgsql/doc/src/sgml/wal.sgml,v 1.68 2010/07/08 16:44:12 momjian Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/wal.sgml,v 1.69 2010/07/16 11:20:23 heikki Exp $ -->
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<chapter id="wal">
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<title>Reliability and the Write-Ahead Log</title>
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<para>
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There will always be at least one WAL segment file, and will normally
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not be more than (2 + <varname>checkpoint_completion_target</varname>) * <varname>checkpoint_segments</varname> + 1
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or <varname>checkpoint_segments</> + <xref linkend="guc-wal-keep-segments"> + 1
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files. Each segment file is normally 16 MB (though this size can be
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altered when building the server). You can use this to estimate space
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requirements for <acronym>WAL</acronym>.
@@ -460,6 +461,22 @@
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of recycled until the system gets back under this limit.
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</para>
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<para>
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In archive recovery or standby mode, the server periodically performs
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<firstterm>restartpoints</><indexterm><primary>restartpoint</></>
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which are similar to checkpoints in normal operation: the server forces
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all its state to disk, updates the <filename>pg_control</> file to
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indicate that the already-processed WAL data need not be scanned again,
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and then recycles any old log segment files in <filename>pg_xlog</>
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directory. A restartpoint is triggered if at least one checkpoint record
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has been replayed and <varname>checkpoint_timeout</> seconds have passed
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since last restartpoint. In standby mode, a restartpoint is also triggered
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if <varname>checkoint_segments</> log segments have been replayed since
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last restartpoint and at least one checkpoint record has been replayed.
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Restartpoints can't be performed more frequently than checkpoints in the
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master because restartpoints can only be performed at checkpoint records.
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</para>
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<para>
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There are two commonly used internal <acronym>WAL</acronym> functions:
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<function>LogInsert</function> and <function>LogFlush</function>.

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