diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/commands/vacuumlazy.c | 20 | ||||
| -rw-r--r-- | src/backend/storage/ipc/procarray.c | 12 |
2 files changed, 30 insertions, 2 deletions
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c index b3e74a62171..034934a56f2 100644 --- a/src/backend/commands/vacuumlazy.c +++ b/src/backend/commands/vacuumlazy.c @@ -349,6 +349,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats, Size freespace; bool all_visible_according_to_vm = false; bool all_visible; + bool has_dead_tuples; /* * Skip pages that don't require vacuuming according to the visibility @@ -500,6 +501,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats, * requiring freezing. */ all_visible = true; + has_dead_tuples = false; nfrozen = 0; hastup = false; prev_dead_count = vacrelstats->num_dead_tuples; @@ -640,6 +642,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats, HeapTupleHeaderAdvanceLatestRemovedXid(tuple.t_data, &vacrelstats->latestRemovedXid); tups_vacuumed += 1; + has_dead_tuples = true; } else { @@ -703,9 +706,22 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats, PageSetAllVisible(page); SetBufferCommitInfoNeedsSave(buf); } - else if (PageIsAllVisible(page) && !all_visible) + /* + * It's possible for the value returned by GetOldestXmin() to move + * backwards, so it's not wrong for us to see tuples that appear to + * not be visible to everyone yet, while PD_ALL_VISIBLE is already + * set. The real safe xmin value never moves backwards, but + * GetOldestXmin() is conservative and sometimes returns a value + * that's unnecessarily small, so if we see that contradiction it + * just means that the tuples that we think are not visible to + * everyone yet actually are, and the PD_ALL_VISIBLE flag is correct. + * + * There should never be dead tuples on a page with PD_ALL_VISIBLE + * set, however. + */ + else if (PageIsAllVisible(page) && has_dead_tuples) { - elog(WARNING, "PD_ALL_VISIBLE flag was incorrectly set in relation \"%s\" page %u", + elog(WARNING, "page containing dead tuples is marked as all-visible in relation \"%s\" page %u", relname, blkno); PageClearAllVisible(page); SetBufferCommitInfoNeedsSave(buf); diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c index 8badd663be4..89ec7f04619 100644 --- a/src/backend/storage/ipc/procarray.c +++ b/src/backend/storage/ipc/procarray.c @@ -1000,6 +1000,18 @@ TransactionIdIsActive(TransactionId xid) * This is also used to determine where to truncate pg_subtrans. allDbs * must be TRUE for that case, and ignoreVacuum FALSE. * + * Note: it's possible for the calculated value to move backwards on repeated + * calls. The calculated value is conservative, so that anything older is + * definitely not considered as running by anyone anymore, but the exact + * value calculated depends on a number of things. For example, if allDbs is + * TRUE and there are no transactions running in the current database, + * GetOldestXmin() returns latestCompletedXid. If a transaction begins after + * that, its xmin will include in-progress transactions in other databases + * that started earlier, so another call will return an lower value. The + * return value is also adjusted with vacuum_defer_cleanup_age, so increasing + * that setting on the fly is an easy way to have GetOldestXmin() move + * backwards. + * * Note: we include all currently running xids in the set of considered xids. * This ensures that if a just-started xact has not yet set its snapshot, * when it does set the snapshot it cannot set xmin less than what we compute. |