On Tue, Dec 26, 2017 at 4:30 PM, Andres Freund <and...@anarazel.de> wrote: > You're proposing to lock the entire relation against many forms of concurrent > DDL, just to get rid of that error? That seems unacceptable. > Isn't the canonical way to solve this to take object locks?
Sure. That's where things in lmgr.c come into play, like LockSharedObject(), and you could hold with an exclusive lock on a given object until the end of a transaction before opening the catalog relation with heap_open(), however with those you need to know the object OID before taking a lock on the parent relation, right? So you face problems with lock upgrades, or race conditions show up more easily. I have to admit that I have not dug much into the problem yet, it is easy enough to have isolation tests by the way, and I just noticed that ALTER DATABASE SET can equally trigger the error. -- Michael
