<sect2 id="logical-replication-publication-replica-identity">

<title>Replica Identity</title>

<para>

A published table must have a <firstterm>replica identity</firstterm>

configured in order to be able to replicate <command>UPDATE</command>

and <command>DELETE</command> operations, so that appropriate rows to

update or delete can be identified on the subscriber side.

</para>

<para>

By default, this is the primary key, if there is one. Another unique index

(with certain additional requirements) can also be set to be the replica

identity. If the table does not have any suitable key, then it can be set

to replica identity <literal>FULL</literal>, which means the entire row

becomes the key. When replica identity <literal>FULL</literal> is

specified, indexes can be used on the subscriber side for searching the

rows. Candidate indexes must be btree or hash, non-partial, and the

leftmost index field must be a column (not an expression) that references

the published table column. These restrictions on the non-unique index

properties adhere to some of the restrictions that are enforced for

primary keys. If there are no such suitable indexes, the search on the

subscriber side can be very inefficient, therefore replica identity

<literal>FULL</literal> should only be used as a fallback if no other

solution is possible.

</para>

<para>

If a replica identity other than <literal>FULL</literal> is set on the

publisher side, a replica identity comprising the same or fewer columns

must also be set on the subscriber side.

</para>

<para>

Tables with a replica identity defined as <literal>NOTHING</literal>,

<literal>DEFAULT</literal> without a primary key, or <literal>USING

INDEX</literal> with a dropped index, cannot support

<command>UPDATE</command> or <command>DELETE</command> operations when

included in a publication replicating these actions. Attempting such

operations will result in an error on the publisher.

</para>

<para>

<command>INSERT</command> operations can proceed regardless of any replica identity.

</para>

<para>

See <link linkend="sql-altertable-replica-identity"><literal>ALTER TABLE...REPLICA IDENTITY</literal></link>

for details on how to set the replica identity.

</para>

</sect2>

Records the old values of the columns of the primary key.

When there is no primary key, the behavior is the same as <literal>NOTHING</literal>.