I have noticed that all SELECT queries alone in a transaction also update pg_stat_database (I know it's just a view that calls pg_stat_get_db_xact_commit()). Does that mean that SELECTs by themselves require a disk write? If so, is that a synchronous disk write? Is it due to something else entirely (like autovacuum or the statistics collector)? Also, is there a way to retrieve the current transaction id? Thanks, Jeff Davis
