DOC: documented track_global_snapshots variable for pg_shardman

Author: Liudmila Mantrova

doc/src/sgml/config.sgml

@@ -8645,6 +8645,32 @@ LOG:  CleanUpLock: deleting: lock(0xb7acd844) id(24688,24696,0,0,0,1)
      </varlistentry>
    </variablelist>
   </sect1>
+
+  <sect1 id="runtime-misc">
+   <title>Miscellaneous</title>
+
+  <variablelist>
+    <varlistentry id="guc-track-global-snapshots" xreflabel="track_global_snapshots">
+    <term>
+     <varname>track_global_snapshots</> (<type>boolean</type>)
+     <indexterm>
+      <primary><varname>track_global_snapshots</> configuration parameter</primary>
+     </indexterm>
+    </term>
+    <listitem>
+     <para>
+      Enables/disables distributed transaction manager based on Clock-SI
+      algorithm. When set to <literal>true</true>, provides cluster-wide
+      transaction isolation at the <literal>Repeatable Read</literal> level.
+     </para>
+     <para>
+      Default: <literal>false</literal>
+     </para>
+    </listitem>
+   </varlistentry>
+  </variablelist>
+  </sect1>
+
   <sect1 id="runtime-config-short">
    <title>Short Options</title>