3 files changed, 93 insertions, 6 deletions
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml
index 0f2397df497..98882ddab86 100644
--- a/doc/src/sgml/fdwhandler.sgml
+++ b/doc/src/sgml/fdwhandler.sgml
@@ -1065,6 +1065,67 @@ EndDirectModify(ForeignScanState *node);
 
    </sect2>
 
+   <sect2 id="fdw-callbacks-truncate">
+    <title>FDW Routines for <command>TRUNCATE</command></title>
+
+    <para>
+<programlisting>
+void
+ExecForeignTruncate(List *rels, List *rels_extra,
+                    DropBehavior behavior, bool restart_seqs);
+</programlisting>
+
+     Truncate a set of foreign tables specified in <literal>rels</literal>.
+     This function is called when <xref linkend="sql-truncate"/> is executed
+     on foreign tables.  <literal>rels</literal> is the list of
+     <structname>Relation</structname> data structure that indicates
+     a foreign table to truncate.  <literal>rels_extra</literal> the list of
+     <literal>int</literal> value, which delivers extra information about
+     a foreign table to truncate.  Possible values are
+     <literal>TRUNCATE_REL_CONTEXT_NORMAL</literal>, which means that
+     the foreign table is specified WITHOUT <literal>ONLY</literal> clause
+     in <command>TRUNCATE</command>,
+     <literal>TRUNCATE_REL_CONTEXT_ONLY</literal>, which means that
+     the foreign table is specified WITH <literal>ONLY</literal> clause,
+     and <literal>TRUNCATE_REL_CONTEXT_CASCADING</literal>,
+     which means that the foreign table is not specified explicitly,
+     but will be truncated due to dependency (for example, partition table).
+     There is one-to-one mapping between <literal>rels</literal> and
+     <literal>rels_extra</literal>.  The number of entries is the same
+     between the two lists.
+    </para>
+
+    <para>
+     <literal>behavior</literal> defines how foreign tables should
+     be truncated, using as possible values <literal>DROP_RESTRICT</literal>,
+     which means that <literal>RESTRICT</literal> option is specified,
+     and <literal>DROP_CASCADE</literal>, which means that
+     <literal>CASCADE</literal> option is specified, in
+     <command>TRUNCATE</command> command.
+    </para>
+    
+    <para>
+     <literal>restart_seqs</literal> is set to <literal>true</literal>
+     if <literal>RESTART IDENTITY</literal> option is specified in
+     <command>TRUNCATE</command> command.  It is <literal>false</literal>
+     if <literal>CONTINUE IDENTITY</literal> option is specified.
+    </para>
+
+    <para>
+     <command>TRUNCATE</command> invokes
+     <function>ExecForeignTruncate</function> once per foreign server
+     that foreign tables to truncate belong to.  This means that all foreign
+     tables included in <literal>rels</literal> must belong to the same
+     server.
+    </para>
+
+    <para>
+     If the <function>ExecForeignTruncate</function> pointer is set to
+     <literal>NULL</literal>, attempts to truncate foreign tables will
+     fail with an error message.
+    </para>
+   </sect2>
+
    <sect2 id="fdw-callbacks-row-locking">
     <title>FDW Routines for Row Locking</title>
 
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index b0792a13b13..fd349569369 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -63,9 +63,10 @@
  <para>
   Now you need only <command>SELECT</command> from a foreign table to access
   the data stored in its underlying remote table.  You can also modify
-  the remote table using <command>INSERT</command>, <command>UPDATE</command>, or
-  <command>DELETE</command>.  (Of course, the remote user you have specified
-  in your user mapping must have privileges to do these things.)
+  the remote table using <command>INSERT</command>, <command>UPDATE</command>,
+  <command>DELETE</command>, or <command>TRUNCATE</command>.
+  (Of course, the remote user you have specified in your user mapping must
+  have privileges to do these things.)
  </para>
 
  <para>
@@ -437,6 +438,31 @@ OPTIONS (ADD password_required 'false');
   </sect3>
 
   <sect3>
+   <title>Truncatability Options</title>
+
+   <para>
+    By default all foreign tables using <filename>postgres_fdw</filename> are assumed
+    to be truncatable.  This may be overridden using the following option:
+   </para>
+
+   <variablelist>
+
+    <varlistentry>
+     <term><literal>truncatable</literal></term>
+     <listitem>
+      <para>
+       This option controls whether <filename>postgres_fdw</filename> allows
+       foreign tables to be truncated using <command>TRUNCATE</command>
+       command. It can be specified for a foreign table or a foreign server.
+       A table-level option overrides a server-level option.
+       The default is <literal>true</literal>.
+      </para>
+     </listitem>
+    </varlistentry>
+   </variablelist>
+  </sect3>
+
+  <sect3>
    <title>Importing Options</title>
 
    <para>
diff --git a/doc/src/sgml/ref/truncate.sgml b/doc/src/sgml/ref/truncate.sgml
index 91cdac55623..acf3633be46 100644
--- a/doc/src/sgml/ref/truncate.sgml
+++ b/doc/src/sgml/ref/truncate.sgml
@@ -172,9 +172,9 @@ TRUNCATE [ TABLE ] [ ONLY ] <replaceable class="parameter">name</replaceable> [
   </para>
 
   <para>
-   <command>TRUNCATE</command> is not currently supported for foreign tables.
-   This implies that if a specified table has any descendant tables that are
-   foreign, the command will fail.
+   <command>TRUNCATE</command> can be used for foreign tables if
+   the foreign data wrapper supports, for instance,
+   see <xref linkend="postgres-fdw"/>.
   </para>
  </refsect1>