Doc: explain the log format of logical replication conflicts.

This commit adds a detailed explanation of the log format for logical
replication conflicts.

Author: Hou Zhijie
Reviewed-by: Shveta Malik, Peter Smith, Hayato Kuroda
Discussion: https://postgr.es/m/OS0PR01MB5716352552DFADB8E9AD1D8994C92@OS0PR01MB5716.jpnprd01.prod.outlook.com
Discussion: https://postgr.es/m/OS0PR01MB57162EDE8BA17F3EE08A24CA948D2@OS0PR01MB5716.jpnprd01.prod.outlook.com

Author: Amit Kapila

doc/src/sgml/logical-replication.sgml

@@ -1666,6 +1666,111 @@ test_sub=# SELECT * FROM t1 ORDER BY id;
     log.
   </para>
 
+  <para>
+   The log format for logical replication conflicts is as follows:
+<synopsis>
+LOG:  conflict detected on relation "<replaceable>schemaname</replaceable>.<replaceable>tablename</replaceable>": conflict=<replaceable>conflict_type</replaceable>
+DETAIL:  <replaceable class="parameter">detailed_explanation</replaceable>.
+{<replaceable class="parameter">detail_values</replaceable> [; ... ]}.
+
+<phrase>where <replaceable class="parameter">detail_values</replaceable> is one of:</phrase>
+
+    <literal>Key</literal> (<replaceable>column_name</replaceable> <optional>, ...</optional>)=(<replaceable>column_value</replaceable> <optional>, ...</optional>)
+    <literal>existing local tuple</literal> <optional>(<replaceable>column_name</replaceable> <optional>, ...</optional>)=</optional>(<replaceable>column_value</replaceable> <optional>, ...</optional>)
+    <literal>remote tuple</literal> <optional>(<replaceable>column_name</replaceable> <optional>, ...</optional>)=</optional>(<replaceable>column_value</replaceable> <optional>, ...</optional>)
+    <literal>replica identity</literal> {(<replaceable>column_name</replaceable> <optional>, ...</optional>)=(<replaceable>column_value</replaceable> <optional>, ...</optional>) | full <optional>(<replaceable>column_name</replaceable> <optional>, ...</optional>)=</optional>(<replaceable>column_value</replaceable> <optional>, ...</optional>)}
+</synopsis>
+
+   The log provides the following information:
+   <variablelist>
+    <varlistentry>
+     <term><literal>LOG</literal></term>
+      <listitem>
+       <itemizedlist>
+        <listitem>
+         <para>
+         <replaceable>schemaname</replaceable>.<replaceable>tablename</replaceable>
+         identifies the local relation involved in the conflict.
+         </para>
+        </listitem>
+        <listitem>
+         <para>
+         <replaceable>conflict_type</replaceable> is the type of conflict that occurred
+         (e.g., <literal>insert_exists</literal>, <literal>update_exists</literal>).
+         </para>
+        </listitem>
+       </itemizedlist>
+      </listitem>
+    </varlistentry>
+
+    <varlistentry>
+     <term><literal>DETAIL</literal></term>
+      <listitem>
+      <itemizedlist>
+       <listitem>
+        <para>
+         <replaceable class="parameter">detailed_explanation</replaceable> includes
+         the origin, transaction ID, and commit timestamp of the transaction that
+         modified the existing local tuple, if available.
+        </para>
+       </listitem>
+       <listitem>
+        <para>
+         The <literal>Key</literal> section includes the key values of the local
+         tuple that violated a unique constraint for
+         <literal>insert_exists</literal> or <literal>update_exists</literal>
+         conflicts.
+        </para>
+       </listitem>
+       <listitem>
+        <para>
+         The <literal>existing local tuple</literal> section includes the local
+         tuple if its origin differs from the remote tuple for
+         <literal>update_differ</literal> or <literal>delete_differ</literal>
+         conflicts, or if the key value conflicts with the remote tuple for
+         <literal>insert_exists</literal> or <literal>update_exists</literal>
+         conflicts.
+        </para>
+       </listitem>
+       <listitem>
+        <para>
+         The <literal>remote tuple</literal> section includes the new tuple from
+         the remote insert or update operation that caused the conflict. Note that
+         for an update operation, the column value of the new tuple will be null
+         if the value is unchanged and toasted.
+        </para>
+       </listitem>
+       <listitem>
+        <para>
+         The <literal>replica identity</literal> section includes the replica
+         identity key values that were used to search for the existing local
+         tuple to be updated or deleted. This may include the full tuple value
+         if the local relation is marked with
+         <link linkend="sql-altertable-replica-identity-full"><literal>REPLICA IDENTITY FULL</literal></link>.
+        </para>
+       </listitem>
+       <listitem>
+        <para>
+         <replaceable class="parameter">column_name</replaceable> is the column name.
+         For <literal>existing local tuple</literal>, <literal>remote tuple</literal>,
+         and <literal>replica identity full</literal> cases, column names are
+         logged only if the user lacks the privilege to access all columns of
+         the table. If column names are present, they appear in the same order
+         as the corresponding column values.
+        </para>
+       </listitem>
+       <listitem>
+        <para>
+         <replaceable class="parameter">column_value</replaceable> is the column value.
+         The large column values are truncated to 64 bytes.
+        </para>
+       </listitem>
+      </itemizedlist>
+     </listitem>
+    </varlistentry>
+   </variablelist>
+  </para>
+
   <para>
    Logical replication operations are performed with the privileges of the role
    which owns the subscription.  Permissions failures on target tables will