docs - clarified system columns not available for queries on replicated tables. (#8259)

gpdb-doc/dita/admin_guide/ddl/ddl-table.xml

@@ -199,6 +199,11 @@
           <li>improve query performance by making it unnecessary to broadcast frequently used tables
             to all segments.</li>
         </ul>
+        <note>The hidden system columns (<codeph>ctid</codeph>, <codeph>cmin</codeph>,
+            <codeph>cmax</codeph>, <codeph>xmin</codeph>, <codeph>xmax</codeph>, and
+            <codeph>gp_segment_id</codeph>) cannot be referenced in user queries on replicated
+          tables because they have no single, unambiguous value. Greenplum Database returns a
+            <codeph>column does not exist</codeph> error for the query.</note>
       </body>
       <topic id="topic35" xml:lang="en">
         <title>Declaring Distribution Keys</title>

gpdb-doc/dita/admin_guide/managing/monitor.xml

@@ -248,12 +248,12 @@ Distributed by: (sale_id)
           </p>
           <p>A table is considered to have a balanced distribution if all segments have roughly the
             same number of rows.</p>
-        <note>
-          <p>If you run this query on a replicated table it fails because Greenplum Database does
-            not permit user queries to reference the <codeph>gp_segment_id</codeph> system column in
-            replicated tables. Because every segment has all of the tables' rows, replicated tables
-            are evenly distributed by definition.</p>
-        </note>
+        <note>If you run this query on a replicated table, it fails because Greenplum Database does
+          not permit user queries to reference the system column <codeph>gp_segment_id</codeph> (or
+          the system columns <codeph>ctid</codeph>, <codeph>cmin</codeph>, <codeph>cmax</codeph>,
+            <codeph>xmin</codeph>, and <codeph>xmax</codeph>) in replicated tables. Because every
+          segment has all of the tables' rows, replicated tables are evenly distributed by
+          definition.</note>
         </body>
       </topic>
       <topic id="topic23" xml:lang="en">

gpdb-doc/dita/admin_guide/query/topics/functions-operators.xml

@@ -147,8 +147,15 @@
                 such as <codeph>setval()</codeph> are not allowed to execute on distributed data in
                 Greenplum Database because they can cause inconsistent data between segment
                 instances.</p>
-            <p>A function can execute read-only queries on replicated tables (<codeph>DISTRIBUTED REPLICATED</codeph>)
-                on the segments, but any SQL command that modifies data must execute on the master instance. </p>
+            <p>A function can execute read-only queries on replicated tables (<codeph>DISTRIBUTED
+                    REPLICATED</codeph>) on the segments, but any SQL command that modifies data
+                must execute on the master instance.
+                <note>The hidden system columns (<codeph>ctid</codeph>, <codeph>cmin</codeph>,
+                        <codeph>cmax</codeph>, <codeph>xmin</codeph>, <codeph>xmax</codeph>, and
+                        <codeph>gp_segment_id</codeph>) cannot be referenced in user queries on
+                    replicated tables because they have no single, unambiguous value. Greenplum
+                    Database returns a <codeph>column does not exist</codeph> error for the
+                    query.</note></p>
             <p>To ensure data consistency, you can safely use <codeph>VOLATILE</codeph> and
                     <codeph>STABLE</codeph> functions in statements that are evaluated on and run
                 from the master. For example, the following statements run on the master (statements

gpdb-doc/dita/ref_guide/sql_commands/CREATE_TABLE.xml

@@ -186,7 +186,8 @@ CREATE [ [GLOBAL | LOCAL] {TEMPORARY | TEMP} | UNLOGGED ] TABLE [IF NOT EXISTS]
         be inherited by another table. The hidden system columns (<codeph>ctid</codeph>,
           <codeph>cmin</codeph>, <codeph>cmax</codeph>, <codeph>xmin</codeph>,
         <codeph>xmax</codeph>, and <codeph>gp_segment_id</codeph>) cannot be referenced in user
-        queries on replicated tables because they have no single, unambiguous value.</p>
+        queries on replicated tables because they have no single, unambiguous value. Greenplum
+        Database returns a <codeph>column does not exist</codeph> error for the query.</p>
       <p>The <codeph>PARTITION BY</codeph> clause allows you to divide the table into multiple
         sub-tables (or parts) that, taken together, make up the parent table and share its schema.
         Though the sub-tables exist as independent tables, the Greenplum Database restricts their