iv></div><p>
   <code class="filename">postgres_fdw</code> can be used with remote servers dating back
   to <span class="productname">PostgreSQL</span> 8.3.  Read-only capability is available
   back to 8.1.  A limitation however is that <code class="filename">postgres_fdw</code>
   generally assumes that immutable built-in functions and operators are
   safe to send to the remote server for execution, if they appear in a
   <code class="literal">WHERE</code> clause for a foreign table.  Thus, a built-in
 