From 9d178fb928040f1a5ab5b566f1ec76d7ac554587 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Thu, 20 Sep 2018 14:02:56 +1200 Subject: [PATCH] Defer restoration of libraries in parallel workers. Several users of extensions complained of crashes in parallel workers that turned out to be due to syscache access from their _PG_init() functions. Reorder the initialization of parallel workers so that libraries are restored after the caches are initialized, and inside a transaction. This was reported in bug #15350 and elsewhere. We don't consider it to be a bug: extensions shouldn't do that, because then they can't be used in shared_preload_libraries. However, it's a fairly obscure hazard and these extensions worked in practice before parallel query came along. So let's make it work. Later commits might add a warning message and eventually an error. Back-patch to 9.6, where parallel query landed. Author: Thomas Munro Reviewed-by: Amit Kapila Reported-by: Kieran McCusker, Jimmy Discussion: https://postgr.es/m/153512195228.1489.8545997741965926448%40wrigleys.postgresql.org --- src/backend/access/transam/parallel.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c index 1d631b7275..a9edf7b9e8 100644 --- a/src/backend/access/transam/parallel.c +++ b/src/backend/access/transam/parallel.c @@ -1303,14 +1303,6 @@ ParallelWorkerMain(Datum main_arg) fps->parallel_master_pid)) return; - /* - * Load libraries that were loaded by original backend. We want to do - * this before restoring GUCs, because the libraries might define custom - * variables. - */ - libraryspace = shm_toc_lookup(toc, PARALLEL_KEY_LIBRARY, false); - RestoreLibraryState(libraryspace); - /* * Identify the entry point to be called. In theory this could result in * loading an additional library, though most likely the entry point is in @@ -1333,9 +1325,17 @@ ParallelWorkerMain(Datum main_arg) */ SetClientEncoding(GetDatabaseEncoding()); + /* + * Load libraries that were loaded by original backend. We want to do + * this before restoring GUCs, because the libraries might define custom + * variables. + */ + libraryspace = shm_toc_lookup(toc, PARALLEL_KEY_LIBRARY, false); + StartTransactionCommand(); + RestoreLibraryState(libraryspace); + /* Restore GUC values from launching backend. */ gucspace = shm_toc_lookup(toc, PARALLEL_KEY_GUC, false); - StartTransactionCommand(); RestoreGUCState(gucspace); CommitTransactionCommand(); -- 2.40.0