/* * For Hot Standby we need to know the highest transaction id that will * be removed by any change. VACUUM proceeds in a number of passes so * we need to consider how each pass operates. The first phase runs * heap_page_prune(), which can issue XLOG_HEAP2_CLEAN records as it * progresses - these will have a latestRemovedXid on each record. * In some cases this removes all of the tuples to be removed, though * often we have dead tuples with index pointers so we must remember them * for removal in phase 3. Index records for those rows are removed * in phase 2 and index blocks do not have MVCC information attached. * So before we can allow removal of any index tuples we need to issue * a WAL record containing the latestRemovedXid of rows that will be * removed in phase three. This allows recovery queries to block at the * correct place, i.e. before phase two, rather than during phase three * which would be after the rows have become inaccessible. */ static void vacuum_log_cleanup_info(Relation rel, LVRelStats *vacrelstats) { /* * Skip this for relations for which no WAL is to be written, or if we're * not trying to support archive recovery. */ if (!RelationNeedsWAL(rel) || !XLogIsNeeded()) return; /* * No need to write the record at all unless it contains a valid value */ if (TransactionIdIsValid(vacrelstats->latestRemovedXid)) (void) log_heap_cleanup_info(rel->rd_node, vacrelstats->latestRemovedXid); }
/* * For Hot Standby we need to know the highest transaction id that will * be removed by any change. VACUUM proceeds in a number of passes so * we need to consider how each pass operates. The first phase runs * heap_page_prune(), which can issue XLOG_HEAP2_CLEAN records as it * progresses - these will have a latestRemovedXid on each record. * In some cases this removes all of the tuples to be removed, though * often we have dead tuples with index pointers so we must remember them * for removal in phase 3. Index records for those rows are removed * in phase 2 and index blocks do not have MVCC information attached. * So before we can allow removal of any index tuples we need to issue * a WAL record containing the latestRemovedXid of rows that will be * removed in phase three. This allows recovery queries to block at the * correct place, i.e. before phase two, rather than during phase three * which would be after the rows have become inaccessible. */ static void vacuum_log_cleanup_info(Relation rel, LVRelStats *vacrelstats) { /* * No need to log changes for temp tables, they do not contain data * visible on the standby server. */ if (rel->rd_istemp || !XLogIsNeeded()) return; /* * No need to write the record at all unless it contains a valid value */ if (TransactionIdIsValid(vacrelstats->latestRemovedXid)) (void) log_heap_cleanup_info(rel->rd_node, vacrelstats->latestRemovedXid); }