diff options
Diffstat (limited to 'src/backend/utils/time/snapmgr.c')
| -rw-r--r-- | src/backend/utils/time/snapmgr.c | 21 |
1 files changed, 18 insertions, 3 deletions
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c index ecc32cb3fe7..67f3e2d667d 100644 --- a/src/backend/utils/time/snapmgr.c +++ b/src/backend/utils/time/snapmgr.c @@ -954,7 +954,12 @@ xmin_cmp(const pairingheap_node *a, const pairingheap_node *b, void *arg) * * If there are no more snapshots, we can reset our PGXACT->xmin to InvalidXid. * Note we can do this without locking because we assume that storing an Xid - * is atomic. + * is atomic. We do this because it will allow multi-statement transactions to + * reset their xmin and prevent us from holding back removal of dead rows; + * this has little purpose when we are dealing with very fast statements in + * read committed mode since the xmin will advance quickly anyway. It has no + * use at all when we are running single statement transactions since the xmin + * is reset as part of end of transaction anyway. * * Even if there are some remaining snapshots, we may be able to advance our * PGXACT->xmin to some degree. This typically happens when a portal is @@ -1051,7 +1056,7 @@ AtSubAbort_Snapshot(int level) * Snapshot manager's cleanup function for end of transaction */ void -AtEOXact_Snapshot(bool isCommit) +AtEOXact_Snapshot(bool isCommit, bool isPrepare) { /* * In transaction-snapshot mode we must release our privately-managed @@ -1136,7 +1141,17 @@ AtEOXact_Snapshot(bool isCommit) FirstSnapshotSet = false; - SnapshotResetXmin(); + /* + * During normal commit and abort processing, we call + * ProcArrayEndTransaction() or ProcArrayClearTransaction() to + * reset the PgXact->xmin. That call happens prior to the call to + * AtEOXact_Snapshot(), so we need not touch xmin here at all, + * accept when we are preparing a transaction. + */ + if (isPrepare) + SnapshotResetXmin(); + + Assert(MyPgXact->xmin == 0); } |