<refsect1>

<title>Notes</title>

<para>

When disabling or enabling checksums in a replication setup of multiple

clusters, it is recommended to stop all the clusters before doing

the switch to all the clusters consistently. When using a replication

setup with tools which perform direct copies of relation file blocks

(for example <xref linkend="app-pgrewind"/>), enabling or disabling

checksums can lead to page corruptions in the shape of incorrect

checksums if the operation is not done consistently across all nodes.

Destroying all the standbys in the setup first, enabling or disabling

checksums on the primary and finally recreating the standbys from

scratch is also safe.

Enabling checksums in a large cluster can potentially take a long time.

During this operation, the cluster or other programs that write to the

data directory must not be started or else data loss may occur.

</para>

<para>

If <application>pg_checksums</application> is aborted or killed in

its operation while enabling or disabling checksums, the cluster

will have the same state with respect of checksums as before the

operation and <application>pg_checksums</application> needs to be

restarted.

When using a replication setup with tools which perform direct copies

of relation file blocks (for example <xref linkend="app-pgrewind"/>),

enabling or disabling checksums can lead to page corruptions in the

shape of incorrect checksums if the operation is not done consistently

across all nodes. When enabling or disabling checksums in a replication

setup, it is thus recommended to stop all the clusters before switching

them all consistently. Destroying all standbys, performing the operation

on the primary and finally recreating the standbys from scratch is also

safe.

</para>

<para>

When enabling checksums in a cluster, the operation can potentially

take a long time if the data directory is large. During this operation,

the cluster or other programs that write to the data directory must not

be started or else data loss may occur.

</para>

If <application>pg_checksums</application> is aborted or killed while

enabling or disabling checksums, the cluster will keep the same

configuration for data checksums as before the operation attempted.

<application>pg_checksums</application> can be restarted to

attempt again the same operation.

</para>

</refsect1>

</refentry>