void
PostgresMain(int argc, char *argv[],
			 const char *dbname,
			 const char *username)
{
    switch (firstchar)
    {
      case 'Q':	/* simple query */
         ……
      case 'M': /* MPP dispatched stmt from QD */
         ……
      case 'T': /* MPP dispatched dtx protocol command from QD */
         ……