ction aborts, all of its child
   subtransactions will also be considered aborted.
  </p><p>
   When a top-level transaction with an xid commits, all of its
   subcommitted child subtransactions are also persistently recorded
   as committed in the <code class="filename">pg_xact</code> subdirectory.  If the
   top-level transaction aborts, all its subtransactions are also aborted,
   even if they were subcommitted.
  </p><p>
   The more subtransactions each transaction keeps open (not
   rolled back or rele