diff options
Diffstat (limited to 'src/backend/access/nbtree/nbtree.c')
| -rw-r--r-- | src/backend/access/nbtree/nbtree.c | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c index 765659887af..03a1d7b027a 100644 --- a/src/backend/access/nbtree/nbtree.c +++ b/src/backend/access/nbtree/nbtree.c @@ -228,6 +228,8 @@ btgettuple(IndexScanDesc scan, ScanDirection dir) BTScanOpaque so = (BTScanOpaque) scan->opaque; bool res; + Assert(scan->heapRelation != NULL); + /* btree indexes are never lossy */ scan->xs_recheck = false; @@ -289,6 +291,8 @@ btgetbitmap(IndexScanDesc scan, TIDBitmap *tbm) int64 ntids = 0; ItemPointer heapTid; + Assert(scan->heapRelation == NULL); + /* Each loop iteration performs another primitive index scan */ do { @@ -393,6 +397,32 @@ btrescan(IndexScanDesc scan, ScanKey scankey, int nscankeys, BTScanPosInvalidate(so->currPos); } + /* + * We prefer to eagerly drop leaf page pins before btgettuple returns. + * This avoids making VACUUM wait to acquire a cleanup lock on the page. + * + * We cannot safely drop leaf page pins during index-only scans due to a + * race condition involving VACUUM setting pages all-visible in the VM. + * It's also unsafe for plain index scans that use a non-MVCC snapshot. + * + * When we drop pins eagerly, the mechanism that marks so->killedItems[] + * index tuples LP_DEAD has to deal with concurrent TID recycling races. + * The scheme used to detect unsafe TID recycling won't work when scanning + * unlogged relations (since it involves saving an affected page's LSN). + * Opt out of eager pin dropping during unlogged relation scans for now + * (this is preferable to opting out of kill_prior_tuple LP_DEAD setting). + * + * Also opt out of dropping leaf page pins eagerly during bitmap scans. + * Pins cannot be held for more than an instant during bitmap scans either + * way, so we might as well avoid wasting cycles on acquiring page LSNs. + * + * See nbtree/README section on making concurrent TID recycling safe. + */ + so->dropPin = (!scan->xs_want_itup && + IsMVCCSnapshot(scan->xs_snapshot) && + RelationNeedsWAL(scan->indexRelation) && + scan->heapRelation != NULL); + so->markItemIndex = -1; so->needPrimScan = false; so->scanBehind = false; |