On Tue, Jul 25, 2023 at 12:57:37PM -0700, Andres Freund wrote: > I just rebased my aio tree over the commit and promptly, on the first run, saw > a hang. I did some debugging on that. Unfortunately repeated runs haven't > repeated that hang, despite quite a bit of trying. > > The symptom I was seeing is that all running backends were stuck in > LWLockWaitForVar(), even though the value they're waiting for had > changed. Which obviously "shouldn't be possible".
Hmm. I've also spent a few days looking at this past report that made the LWLock part what it is today, but I don't quite see immediately how it would be possible to reach a state where all the backends are waiting for an update that's not happening: https://www.postgresql.org/message-id/CAMkU=1zlztrowh3b42oxsb04r9zmesk3658qen4_8+b+k3e...@mail.gmail.com All the assumptions of this code and its dependencies with xloginsert.c are hard to come by. > It's of course possible that this is AIO specific, but I didn't see anything > in stacks to suggest that. Or AIO handles the WAL syncs so quickly that it has more chances in showing a race condition here? > I do wonder if this possibly exposed an undocumented prior dependency on the > value update always happening under the list lock. I would not be surprised by that. -- Michael
signature.asc
Description: PGP signature