From 99c1c7846b97446c48bb1ca262218d83b5dd5bf1 Mon Sep 17 00:00:00 2001 From: ashu Date: Fri, 11 Aug 2017 17:59:47 +0530 Subject: [PATCH] Improve locking startegy during VACUUM in Hash Index for regular tables. Patch by Ashutosh Sharma --- src/backend/access/hash/README | 2 +- src/backend/access/hash/hash.c | 44 ++++++++++++++++++++++++++------------ src/backend/access/hash/hashovfl.c | 4 +--- 3 files changed, 32 insertions(+), 18 deletions(-) diff --git a/src/backend/access/hash/README b/src/backend/access/hash/README index eef7d66..34a84ce 100644 --- a/src/backend/access/hash/README +++ b/src/backend/access/hash/README @@ -396,8 +396,8 @@ The fourth operation is garbage collection (bulk deletion): mark the target page dirty write WAL for deleting tuples from target page if this is the last bucket page, break out of loop - pin and x-lock next page release prior lock and pin (except keep pin on primary bucket page) + pin and x-lock next page if the page we have locked is not the primary bucket page: release lock and take exclusive lock on primary bucket page if there are no other pins on the primary bucket page: diff --git a/src/backend/access/hash/hash.c b/src/backend/access/hash/hash.c index 45a3a5a..012e00f 100644 --- a/src/backend/access/hash/hash.c +++ b/src/backend/access/hash/hash.c @@ -660,11 +660,9 @@ hashvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats) * that the next valid TID will be greater than or equal to the current * valid TID. There can't be any concurrent scans in progress when we first * enter this function because of the cleanup lock we hold on the primary - * bucket page, but as soon as we release that lock, there might be. We - * handle that by conspiring to prevent those scans from passing our cleanup - * scan. To do that, we lock the next page in the bucket chain before - * releasing the lock on the previous page. (This type of lock chaining is - * not ideal, so we might want to look for a better solution at some point.) + * bucket page, but as soon as we release that lock, there might be. But, + * we do not have to bother about it, as the hash index scan work in page + * at a time mode. * * We need to retain a pin on the primary bucket to ensure that no concurrent * split can start. @@ -833,18 +831,36 @@ hashbucketcleanup(Relation rel, Bucket cur_bucket, Buffer bucket_buf, if (!BlockNumberIsValid(blkno)) break; - next_buf = _hash_getbuf_with_strategy(rel, blkno, HASH_WRITE, - LH_OVERFLOW_PAGE, - bstrategy); - /* - * release the lock on previous page after acquiring the lock on next - * page + * As the hash index scan works in page-at-a-time mode, vacuum can + * release the lock on previous page before acquiring lock on the next + * page for regular tables, but, for unlogged tables, we avoid this as + * we do not want scan to cross vacuum when both are running on the + * same bucket page. This is to ensure that, we are safe during dead + * marking of index tuples in _hash_kill_items(). */ - if (retain_pin) - LockBuffer(buf, BUFFER_LOCK_UNLOCK); + if (RelationNeedsWAL(rel)) + { + if (retain_pin) + LockBuffer(buf, BUFFER_LOCK_UNLOCK); + else + _hash_relbuf(rel, buf); + + next_buf = _hash_getbuf_with_strategy(rel, blkno, HASH_WRITE, + LH_OVERFLOW_PAGE, + bstrategy); + } else - _hash_relbuf(rel, buf); + { + next_buf = _hash_getbuf_with_strategy(rel, blkno, HASH_WRITE, + LH_OVERFLOW_PAGE, + bstrategy); + + if (retain_pin) + LockBuffer(buf, BUFFER_LOCK_UNLOCK); + else + _hash_relbuf(rel, buf); + } buf = next_buf; } diff --git a/src/backend/access/hash/hashovfl.c b/src/backend/access/hash/hashovfl.c index c206e70..3a7011d 100644 --- a/src/backend/access/hash/hashovfl.c +++ b/src/backend/access/hash/hashovfl.c @@ -790,9 +790,7 @@ _hash_initbitmapbuffer(Buffer buf, uint16 bmsize, bool initpage) * Caller must acquire cleanup lock on the primary page of the target * bucket to exclude any scans that are in progress, which could easily * be confused into returning the same tuple more than once or some tuples - * not at all by the rearrangement we are performing here. To prevent - * any concurrent scan to cross the squeeze scan we use lock chaining - * similar to hasbucketcleanup. Refer comments atop hashbucketcleanup. + * not at all by the rearrangement we are performing here. * * We need to retain a pin on the primary bucket to ensure that no concurrent * split can start. -- 1.8.3.1