index 8dfb01a77be09a6b1ba0104f89643f232460b67c..a2571d33ae67d61724eb384afb00e3d3580a242a 100644 (file)
<para>
<filename>amcheck</filename> can be effective at detecting various types of
failure modes that <link
- linkend="app-initdb-data-checksums"><application>data page
+ linkend="app-initdb-data-checksums"><application>data
checksums</application></link> will fail to catch. These include:
<itemizedlist>
Structural corruption can happen due to faulty storage hardware, or
relation files being overwritten or modified by unrelated software.
This kind of corruption can also be detected with
- <link linkend="
app-initdb-data-checksums"><application>data page
+ <link linkend="checksums"><application>data page
checksums</application></link>.
</para>
index f4bc147b10684feb3f44a49867fe0375a0e21bb1..66de1ee2f81cbf57f3607a997bd67a67812c76c1 100644 (file)
Data pages are not currently checksummed by default, though full page images
recorded in WAL records will be protected; see <link
linkend="app-initdb-data-checksums"><application>initdb</application></link>
- for details about enabling data page checksums.
+ for details about enabling data checksums.
</para>
</listitem>
<listitem>
</para>
</sect1>
+ <sect1 id="checksums">
+ <title>Data Checksums</title>
+ <indexterm>
+ <primary>checksums</primary>
+ </indexterm>
+
+ <para>
+ Data pages are not checksum protected by default, but this can optionally be
+ enabled for a cluster. When enabled, each data page will be assigned a
+ checksum that is updated when the page is written and verified every time
+ the page is read. Only data pages are protected by checksums, internal data
+ structures and temporary files are not.
+ </para>
+
+ <para>
+ Checksums are normally enabled when the cluster is initialized using <link
+ linkend="app-initdb-data-checksums"><application>initdb</application></link>.
+ They can also be enabled or disabled at a later time as an offline
+ operation. Data checksums are enabled or disabled at the full cluster
+ level, and cannot be specified individually for databases or tables.
+ </para>
+
+ <para>
+ The current state of checksums in the cluster can be verified by viewing the
+ value of the read-only configuration variable <xref
+ linkend="guc-data-checksums" /> by issuing the command <command>SHOW
+ data_checksums</command>.
+ </para>
+
+ <para>
+ When attempting to recover from corrupt data it may be necessary to bypass
+ the checksum protection in order to recover data. To do this, temporarily
+ set the configuration parameter <xref linkend="guc-ignore-checksum-failure" />.
+ </para>
+
+ <sect2 id="checksums-offline-enable-disable">
+ <title>Off-line Enabling of Checksums</title>
+
+ <para>
+ The <link linkend="app-pgchecksums"><application>pg_checksums</application></link>
+ application can be used to enable or disable data checksums, as well as
+ verify checksums, on an offline cluster.
+ </para>
+
+ </sect2>
+ </sect1>
+
<sect1 id="wal-intro">
<title>Write-Ahead Logging (<acronym>WAL</acronym>)</title>