diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/access/nbtree/nbtutils.c | 26 |
1 files changed, 21 insertions, 5 deletions
diff --git a/src/backend/access/nbtree/nbtutils.c b/src/backend/access/nbtree/nbtutils.c index aaa0c89c7dd..86cec248593 100644 --- a/src/backend/access/nbtree/nbtutils.c +++ b/src/backend/access/nbtree/nbtutils.c @@ -1725,6 +1725,7 @@ _bt_killitems(IndexScanDesc scan) int i; int numKilled = so->numKilled; bool killedsomething = false; + bool droppedpin PG_USED_FOR_ASSERTS_ONLY; Assert(BTScanPosIsValid(so->currPos)); @@ -1742,6 +1743,7 @@ _bt_killitems(IndexScanDesc scan) * re-use of any TID on the page, so there is no need to check the * LSN. */ + droppedpin = false; LockBuffer(so->currPos.buf, BT_READ); page = BufferGetPage(so->currPos.buf); @@ -1750,6 +1752,7 @@ _bt_killitems(IndexScanDesc scan) { Buffer buf; + droppedpin = true; /* Attempt to re-read the buffer, getting pin and lock. */ buf = _bt_getbuf(scan->indexRelation, so->currPos.currPage, BT_READ); @@ -1795,9 +1798,18 @@ _bt_killitems(IndexScanDesc scan) int j; /* - * Note that we rely on the assumption that heap TIDs in the - * scanpos items array are always in ascending heap TID order - * within a posting list + * We rely on the convention that heap TIDs in the scanpos + * items array are stored in ascending heap TID order for a + * group of TIDs that originally came from a posting list + * tuple. This convention even applies during backwards + * scans, where returning the TIDs in descending order might + * seem more natural. This is about effectiveness, not + * correctness. + * + * Note that the page may have been modified in almost any way + * since we first read it (in the !droppedpin case), so it's + * possible that this posting list tuple wasn't a posting list + * tuple when we first encountered its heap TIDs. */ for (j = 0; j < nposting; j++) { @@ -1806,8 +1818,12 @@ _bt_killitems(IndexScanDesc scan) if (!ItemPointerEquals(item, &kitem->heapTid)) break; /* out of posting list loop */ - /* kitem must have matching offnum when heap TIDs match */ - Assert(kitem->indexOffset == offnum); + /* + * kitem must have matching offnum when heap TIDs match, + * though only in the common case where the page can't + * have been concurrently modified + */ + Assert(kitem->indexOffset == offnum || !droppedpin); /* * Read-ahead to later kitems here. |