diff options
Diffstat (limited to 'src/backend/utils/time/snapmgr.c')
| -rw-r--r-- | src/backend/utils/time/snapmgr.c | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c index e1caf01c603..4bddaed33ba 100644 --- a/src/backend/utils/time/snapmgr.c +++ b/src/backend/utils/time/snapmgr.c @@ -188,6 +188,9 @@ typedef struct ActiveSnapshotElt /* Top of the stack of active snapshots */ static ActiveSnapshotElt *ActiveSnapshot = NULL; +/* Bottom of the stack of active snapshots */ +static ActiveSnapshotElt *OldestActiveSnapshot = NULL; + /* * Currently registered Snapshots. Ordered in a heap by xmin, so that we can * quickly find the one with lowest xmin, to advance our MyPgXat->xmin. @@ -394,6 +397,34 @@ GetLatestSnapshot(void) } /* + * GetOldestSnapshot + * + * Get the oldest known snapshot, as judged by the LSN. + */ +Snapshot +GetOldestSnapshot(void) +{ + Snapshot OldestRegisteredSnapshot = NULL; + XLogRecPtr RegisteredLSN = InvalidXLogRecPtr; + XLogRecPtr ActiveLSN = InvalidXLogRecPtr; + + if (!pairingheap_is_empty(&RegisteredSnapshots)) + { + OldestRegisteredSnapshot = pairingheap_container(SnapshotData, ph_node, + pairingheap_first(&RegisteredSnapshots)); + RegisteredLSN = OldestRegisteredSnapshot->lsn; + } + + if (OldestActiveSnapshot != NULL) + ActiveLSN = OldestActiveSnapshot->as_snap->lsn; + + if (XLogRecPtrIsInvalid(RegisteredLSN) || RegisteredLSN > ActiveLSN) + return OldestActiveSnapshot->as_snap; + + return OldestRegisteredSnapshot; +} + +/* * GetCatalogSnapshot * Get a snapshot that is sufficiently up-to-date for scan of the * system catalog with the specified OID. @@ -674,6 +705,8 @@ PushActiveSnapshot(Snapshot snap) newactive->as_snap->active_count++; ActiveSnapshot = newactive; + if (OldestActiveSnapshot == NULL) + OldestActiveSnapshot = ActiveSnapshot; } /* @@ -744,6 +777,8 @@ PopActiveSnapshot(void) pfree(ActiveSnapshot); ActiveSnapshot = newstack; + if (ActiveSnapshot == NULL) + OldestActiveSnapshot = NULL; SnapshotResetXmin(); } @@ -953,6 +988,8 @@ AtSubAbort_Snapshot(int level) pfree(ActiveSnapshot); ActiveSnapshot = next; + if (ActiveSnapshot == NULL) + OldestActiveSnapshot = NULL; } SnapshotResetXmin(); @@ -1037,6 +1074,7 @@ AtEOXact_Snapshot(bool isCommit) * it'll go away with TopTransactionContext. */ ActiveSnapshot = NULL; + OldestActiveSnapshot = NULL; pairingheap_reset(&RegisteredSnapshots); CurrentSnapshot = NULL; |