stand that there are only limited
   guarantees around the stability of the <code class="structfield">queryid</code> hash
   value.  Since the identifier is derived from the
   post-parse-analysis tree, its value is a function of, among other
   things, the internal object identifiers appearing in this representation.
   This has some counterintuitive implications.  For example,
   <code class="filename">pg_stat_statements</code> will consider two apparently-identical
   queries to be distinct, if they refe