Add the notion of REPLICA IDENTITY for a table.

Pending patches for logical replication will use this to determine
which columns of a tuple ought to be considered as its candidate key.

Andres Freund, with minor, mostly cosmetic adjustments by me

2 files changed, 43 insertions, 0 deletions

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 9af4697a47b..9388df5ac27 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -1863,6 +1863,19 @@
      </row>
 
      <row>
+      <entry><structfield>relreplident</structfield></entry>
+      <entry><type>char</type></entry>
+      <entry></entry>
+      <entry>
+       Columns used to form <quote>replica identity</> for rows:
+       <literal>d</> = default (primary key, if any),
+       <literal>n</> = nothing,
+       <literal>f</> = all columns
+       <literal>i</> = index with indisreplident set, or default
+      </entry>
+     </row>
+
+     <row>
       <entry><structfield>relfrozenxid</structfield></entry>
       <entry><type>xid</type></entry>
       <entry></entry>
@@ -3658,6 +3671,17 @@
      </row>
 
      <row>
+      <entry><structfield>indisreplident</structfield></entry>
+      <entry><type>bool</type></entry>
+      <entry></entry>
+      <entry>
+       If true this index has been chosen as <quote>replica identity</>
+       using <command>ALTER TABLE ... REPLICA IDENTITY USING INDEX
+       ...</>
+      </entry>
+     </row>
+
+     <row>
       <entry><structfield>indkey</structfield></entry>
       <entry><type>int2vector</type></entry>
       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 2609d4a8eaf..89649a2aa48 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -69,6 +69,7 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
     NOT OF
     OWNER TO <replaceable class="PARAMETER">new_owner</replaceable>
     SET TABLESPACE <replaceable class="PARAMETER">new_tablespace</replaceable>
+    REPLICA IDENTITY {DEFAULT | USING INDEX <replaceable class="PARAMETER">index_name</replaceable> | FULL | NOTHING}
 
 <phrase>and <replaceable class="PARAMETER">table_constraint_using_index</replaceable> is:</phrase>
 
@@ -580,6 +581,24 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
    </varlistentry>
 
    <varlistentry>
+    <term><literal>REPLICA IDENTITY</literal></term>
+    <listitem>
+     <para>
+      This form changes the information which is written to the write-ahead log
+      to identify rows which are updated or deleted.  This option has no effect
+      except when logical replication is in use.  <literal>DEFAULT</> records the 
+      old values of the columns of the primary key, if any.  <literal>USING INDEX</>
+      records the old values of the columns covered by the named index, which
+      must be unique, not partial, not deferrable, and include only columns marked
+      <literal>NOT NULL</>.  <literal>FULL</> records the old values of all columns
+      in the row.  <literal>NOTHING</> records no information about the old row.
+      In all cases, no old values are logged unless at least one of the columns
+      that would be logged differs between the old and new versions of the row.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><literal>RENAME</literal></term>
     <listitem>
      <para>