diff options
| -rw-r--r-- | src/backend/access/heap/heapam.c | 40 | ||||
| -rw-r--r-- | src/backend/access/heap/heapam_handler.c | 15 | ||||
| -rw-r--r-- | src/include/access/heapam.h | 3 |
3 files changed, 43 insertions, 15 deletions
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index 763dc07361e..64b9ec0376a 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -1576,10 +1576,13 @@ heap_getnextslot_tidrange(TableScanDesc sscan, ScanDirection direction, * must unpin the buffer when done with the tuple. * * If the tuple is not found (ie, item number references a deleted slot), - * then tuple->t_data is set to NULL and false is returned. + * then tuple->t_data is set to NULL, *userbuf is set to InvalidBuffer, + * and false is returned. * * If the tuple is found but fails the time qual check, then false is returned - * but tuple->t_data is left pointing to the tuple. + * and *userbuf is set to InvalidBuffer, but tuple->t_data is left pointing + * to the tuple. (Note that it is unsafe to dereference tuple->t_data in + * this case, but callers might choose to test it for NULL-ness.) * * heap_fetch does not follow HOT chains: only the exact TID requested will * be fetched. @@ -1599,6 +1602,25 @@ heap_fetch(Relation relation, HeapTuple tuple, Buffer *userbuf) { + return heap_fetch_extended(relation, snapshot, tuple, userbuf, false); +} + +/* + * heap_fetch_extended - fetch tuple even if it fails snapshot test + * + * If keep_buf is true, then upon finding a tuple that is valid but fails + * the snapshot check, we return the tuple pointer in tuple->t_data and the + * buffer ID in *userbuf, keeping the buffer pin, just as if it had passed + * the snapshot. (The function result is still "false" though.) + * If keep_buf is false then this behaves identically to heap_fetch(). + */ +bool +heap_fetch_extended(Relation relation, + Snapshot snapshot, + HeapTuple tuple, + Buffer *userbuf, + bool keep_buf) +{ ItemPointer tid = &(tuple->t_self); ItemId lp; Buffer buffer; @@ -1680,9 +1702,14 @@ heap_fetch(Relation relation, return true; } - /* Tuple failed time qual */ - ReleaseBuffer(buffer); - *userbuf = InvalidBuffer; + /* Tuple failed time qual, but maybe caller wants to see it anyway. */ + if (keep_buf) + *userbuf = buffer; + else + { + ReleaseBuffer(buffer); + *userbuf = InvalidBuffer; + } return false; } @@ -1705,8 +1732,7 @@ heap_fetch(Relation relation, * are vacuumable, false if not. * * Unlike heap_fetch, the caller must already have pin and (at least) share - * lock on the buffer; it is still pinned/locked at exit. Also unlike - * heap_fetch, we do not report any pgstats count; caller may do so if wanted. + * lock on the buffer; it is still pinned/locked at exit. */ bool heap_hot_search_buffer(ItemPointer tid, Relation relation, Buffer buffer, diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c index d1192e6a0c5..66339392d75 100644 --- a/src/backend/access/heap/heapam_handler.c +++ b/src/backend/access/heap/heapam_handler.c @@ -401,7 +401,8 @@ tuple_lock_retry: errmsg("tuple to be locked was already moved to another partition due to concurrent update"))); tuple->t_self = *tid; - if (heap_fetch(relation, &SnapshotDirty, tuple, &buffer)) + if (heap_fetch_extended(relation, &SnapshotDirty, tuple, + &buffer, true)) { /* * If xmin isn't what we're expecting, the slot must have @@ -500,6 +501,7 @@ tuple_lock_retry: */ if (tuple->t_data == NULL) { + Assert(!BufferIsValid(buffer)); return TM_Deleted; } @@ -509,8 +511,7 @@ tuple_lock_retry: if (!TransactionIdEquals(HeapTupleHeaderGetXmin(tuple->t_data), priorXmax)) { - if (BufferIsValid(buffer)) - ReleaseBuffer(buffer); + ReleaseBuffer(buffer); return TM_Deleted; } @@ -526,13 +527,12 @@ tuple_lock_retry: * * As above, it should be safe to examine xmax and t_ctid * without the buffer content lock, because they can't be - * changing. + * changing. We'd better hold a buffer pin though. */ if (ItemPointerEquals(&tuple->t_self, &tuple->t_data->t_ctid)) { /* deleted, so forget about it */ - if (BufferIsValid(buffer)) - ReleaseBuffer(buffer); + ReleaseBuffer(buffer); return TM_Deleted; } @@ -540,8 +540,7 @@ tuple_lock_retry: *tid = tuple->t_data->t_ctid; /* updated row should have xmin matching this xmax */ priorXmax = HeapTupleHeaderGetUpdateXid(tuple->t_data); - if (BufferIsValid(buffer)) - ReleaseBuffer(buffer); + ReleaseBuffer(buffer); /* loop back to fetch next in chain */ } } diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h index e63b49fc385..4f1dff9ca1b 100644 --- a/src/include/access/heapam.h +++ b/src/include/access/heapam.h @@ -134,6 +134,9 @@ extern bool heap_getnextslot_tidrange(TableScanDesc sscan, TupleTableSlot *slot); extern bool heap_fetch(Relation relation, Snapshot snapshot, HeapTuple tuple, Buffer *userbuf); +extern bool heap_fetch_extended(Relation relation, Snapshot snapshot, + HeapTuple tuple, Buffer *userbuf, + bool keep_buf); extern bool heap_hot_search_buffer(ItemPointer tid, Relation relation, Buffer buffer, Snapshot snapshot, HeapTuple heapTuple, bool *all_dead, bool first_call); |