diff options
Diffstat (limited to 'src/backend/commands/vacuum.c')
| -rw-r--r-- | src/backend/commands/vacuum.c | 20 |
1 files changed, 11 insertions, 9 deletions
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index 395e75f768f..f1112111de8 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -1712,13 +1712,6 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams *params) /* Begin a transaction for vacuuming this relation */ StartTransactionCommand(); - /* - * Need to acquire a snapshot to prevent pg_subtrans from being truncated, - * cutoff xids in local memory wrapping around, and to have updated xmin - * horizons. - */ - PushActiveSnapshot(GetTransactionSnapshot()); - if (!(params->options & VACOPT_FULL)) { /* @@ -1739,9 +1732,11 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams *params) * Note: these flags remain set until CommitTransaction or * AbortTransaction. We don't want to clear them until we reset * MyProc->xid/xmin, otherwise GetOldestNonRemovableTransactionId() - * might appear to go backwards, which is probably Not Good. + * might appear to go backwards, which is probably Not Good. (We also + * set PROC_IN_VACUUM *before* taking our own snapshot, so that our + * xmin doesn't become visible ahead of setting the flag.) */ - LWLockAcquire(ProcArrayLock, LW_SHARED); + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); MyProc->statusFlags |= PROC_IN_VACUUM; if (params->is_wraparound) MyProc->statusFlags |= PROC_VACUUM_FOR_WRAPAROUND; @@ -1750,6 +1745,13 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams *params) } /* + * Need to acquire a snapshot to prevent pg_subtrans from being truncated, + * cutoff xids in local memory wrapping around, and to have updated xmin + * horizons. + */ + PushActiveSnapshot(GetTransactionSnapshot()); + + /* * Check for user-requested abort. Note we want this to be inside a * transaction, so xact.c doesn't issue useless WARNING. */ |