From 0bef1c0678d94436f80450d562a866bb6fa5e509 Mon Sep 17 00:00:00 2001 From: Teodor Sigaev Date: Fri, 4 May 2018 11:27:50 +0300 Subject: Re-think predicate locking on GIN indexes. The principle behind the locking was not very well thought-out, and not documented. Add a section in the README to explain how it's supposed to work, and change the code so that it actually works that way. This fixes two bugs: 1. If fast update was turned on concurrently, subsequent inserts to the pending list would not conflict with predicate locks that were acquired earlier, on entry pages. The included 'predicate-gin-fastupdate' test demonstrates that. To fix, make all scans acquire a predicate lock on the metapage. That lock represents a scan of the pending list, whether or not there is a pending list at the moment. Forget about the optimization to skip locking/checking for locks, when fastupdate=off. 2. If a scan finds no match, it still needs to lock the entry page. The point of predicate locks is to lock the gabs between values, whether or not there is a match. The included 'predicate-gin-nomatch' test tests that case. In addition to those two bug fixes, this removes some unnecessary locking, following the principle laid out in the README. Because all items in a posting tree have the same key value, a lock on the posting tree root is enough to cover all the items. (With a very large posting tree, it would possibly be better to lock the posting tree leaf pages instead, so that a "skip scan" with a query like "A & B", you could avoid unnecessary conflict if a new tuple is inserted with A but !B. But let's keep this simple.) Also, some spelling fixes. Author: Heikki Linnakangas with some editorization by me Review: Andrey Borodin, Alexander Korotkov Discussion: https://www.postgresql.org/message-id/0b3ad2c2-2692-62a9-3a04-5724f2af9114@iki.fi --- src/backend/access/gist/gist.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'src/backend/access/gist/gist.c') diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c index f7a9168925..8a42effdf7 100644 --- a/src/backend/access/gist/gist.c +++ b/src/backend/access/gist/gist.c @@ -1220,7 +1220,7 @@ gistinserttuples(GISTInsertState *state, GISTInsertStack *stack, bool is_split; /* - * Check for any rw conflicts (in serialisation isolation level) just + * Check for any rw conflicts (in serializable isolation level) just * before we intend to modify the page */ CheckForSerializableConflictIn(state->r, NULL, stack->buffer); -- cgit v1.2.1