Re: Getting rid of "tuple concurrently updated" elog()s with concurrent DDLs (at least ALTER TABLE)

On Tue, Dec 26, 2017 at 4:30 PM, Andres Freund <andres(at)anarazel(dot)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