DOC: documented new postgres-fdw gucs required for shardman

Author: Liudmila Mantrova

doc/src/sgml/postgres-fdw.sgml

@@ -599,6 +599,54 @@
   </para>
  </sect2>
 
+ <sect2>
+  <title>GUC Variables</title>
+
+  <variablelist>
+   <varlistentry id="guc-postgres-fdw-use-twophase" xreflabel="postgres_fdw.use_twophase">
+    <term>
+     <varname>postgres_fdw.use_twophase</> (<type>boolean</type>)
+     <indexterm>
+      <primary><varname>postgres_fdw.use_twophase</> configuration parameter</primary>
+     </indexterm>
+    </term>
+    <listitem>
+     <para>
+      Enables two-phase commit (2PC) transactions. If this variable is set to
+      <literal>true</literal>, each transaction must be <firstterm>prepared</firstterm> on all
+       nodes before the commit. A successful <literal>PREPARE</literal>
+       on the node means that this node is ready to commit the transaction,
+       but it will only be committed if all other nodes can commit this
+       transaction as well. Otherwise, the transaction will be aborted.
+       This approach allows to ensure data consistency across all nodes.
+     </para>
+     <para>
+      Default: <literal>false</literal>
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry id="guc-postgres-fdw-use-global-snapshots" xreflabel="postgres_fdw.use_global_snapshots">
+    <term>
+     <varname>postgres_fdw.use_global_snapshots</> (<type>boolean</type>)
+     <indexterm>
+      <primary><varname>postgres_fdw.use_global_snapshots</> configuration parameter</primary>
+     </indexterm>
+    </term>
+    <listitem>
+     <para>
+      Enables/disables distributed transaction manager based on
+      Clock-SI algorithm. When enabled, provides cluster-wide transaction
+      isolation at the <literal>REPEATABLE READ</literal> level.
+     </para>
+     <para>
+      Default: <literal>false</literal>
+     </para>
+    </listitem>
+   </varlistentry>
+  </variablelist>
+ </sect2>
+
  <sect2>
   <title>Examples</title>