From 4974d7f87e62a58e80c6524e49677cb25cc10e12 Mon Sep 17 00:00:00 2001 From: Peter Geoghegan Date: Fri, 10 Aug 2018 13:01:34 -0700 Subject: Handle parallel index builds on mapped relations. Commit 9da0cc35284, which introduced parallel CREATE INDEX, failed to propagate relmapper.c backend local cache state to parallel worker processes. This could result in parallel index builds against mapped catalog relations where the leader process (participating as a worker) scans the new, pristine relfilenode, while worker processes scan the obsolescent relfilenode. When this happened, the final index structure was typically not consistent with the owning table's structure. The final index structure could contain entries formed from both heap relfilenodes. Only rebuilds on mapped catalog relations that occur as part of a VACUUM FULL or CLUSTER could become corrupt in practice, since their mapped relation relfilenode swap is what allows the inconsistency to arise. On master, fix the problem by propagating the required relmapper.c backend state as part of standard parallel initialization (Cf. commit 29d58fd3). On v11, simply disallow builds against mapped catalog relations by deeming them parallel unsafe. Author: Peter Geoghegan Reported-By: "death lock" Reviewed-By: Tom Lane, Amit Kapila Bug: #15309 Discussion: https://postgr.es/m/153329671686.1405.18298309097348420351@wrigleys.postgresql.org Backpatch: 11-, where parallel CREATE INDEX was introduced. --- src/backend/access/transam/README.parallel | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'src/backend/access/transam/README.parallel') diff --git a/src/backend/access/transam/README.parallel b/src/backend/access/transam/README.parallel index f09a5806345..85e5840feba 100644 --- a/src/backend/access/transam/README.parallel +++ b/src/backend/access/transam/README.parallel @@ -125,6 +125,10 @@ worker. This includes: - State related to pending REINDEX operations, which prevents access to an index that is currently being rebuilt. + - Active relmapper.c mapping state. This is needed to allow consistent + answers when fetching the current relfilenode for relation oids of + mapped relations. + To prevent unprincipled deadlocks when running in parallel mode, this code also arranges for the leader and all workers to participate in group locking. See src/backend/storage/lmgr/README for more details. -- cgit v1.2.3