</indexterm>

<para>

By default, data pages are not protected by checksums, but this can optionally be

enabled for a cluster.When enabled, each data pagewill be ASSIGNED a

checksum that is updated when the page is written and verified each time

By default, data pages are not protected by checksums, but this can

optionally beenabled for a cluster. When enabled, each data pageincludes

achecksum that is updated when the page is written and verified each time

the page is read. Only data pages are protected by checksums; internal data

structures and temporary files are not.

</para>

<para>

Checksumsverification isnormallyENABLED when the cluster is initialized using <link

Checksumsarenormallyenabled 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 specifiedfor individual databases or tables.

level, and cannot be specifiedindividually for databases or tables.

</para>

<para>

</para>

<para>

When attempting to recover fromcorrupt data, it may be necessary to bypass

the checksum protection. To do this, temporarily set the configuration

parameter <xref linkend="guc-ignore-checksum-failure" />.

When attempting to recover frompage corruptions, it may be necessary to

bypassthe checksum protection. To do this, temporarily set the

configurationparameter <xref linkend="guc-ignore-checksum-failure" />.

</para>

<sect2 id="checksums-offline-enable-disable">