Fix ALTER COLUMN TYPE to not open a relation without any lock. If the column being modified is referenced by a foreign key constraint of another table, ALTER TABLE would open the other table (to re-parse the constraint's definition) without having first obtained a lock on it. This was evidently intentional, but that doesn't mean it's really safe. It's especially not safe in 9.3, which pre-dates use of MVCC scans for catalog reads, but even in current releases it doesn't seem like a good idea.
We know we'll need AccessExclusiveLock shortly to drop the obsoleted constraint, so just get that a little sooner to close the hole. Per testing with a patch that complains if we open a relation without holding any lock on it. I don't plan to back-patch that patch, but we should close the holes it identifies in all supported branches. Discussion: https://postgr.es/m/2038.1538335...@sss.pgh.pa.us Branch ------ REL9_6_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/0360c539f2a2a979a98b9bb4ae4b3d8b77ee199b Modified Files -------------- src/backend/commands/tablecmds.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)
