On Fri, Apr 20, 2018, at 00:42, Thomas Munro wrote: > On Wed, Apr 18, 2018 at 11:43 AM, Jonathan Rudenberg > <jonat...@titanous.com> wrote: > > On Tue, Apr 17, 2018, at 19:31, Thomas Munro wrote: > >> On Wed, Apr 18, 2018 at 11:01 AM, Jonathan Rudenberg > >> <jonat...@titanous.com> wrote: > >> > Yep, I think I know approximately what it looked like, I've attached a > >> > lightly redacted plan. All of the hung queries were running some variant > >> > of this plan as far as I can tell. > >> > >> Hmm, that isn't a parallel query. I was expecting to see "Gather" and > >> "Parallel" in there. > > > > Oops, I'm really sorry about that. I only have the first part of the hung > > queries, and there are a few variants. Here's one that's parallel. > > I spent some time trying to reproduce this failure without any luck, > using query plans similar to your Gather plan fragment, and using some > test harness code for the allocator stuff in isolation. > > I had an idea that (1) freeing a large object that releases and unpins > a segment in one backend and then (2) freeing it again in another > backend (illegally) might produce this effect with sufficiently bad > luck. I'm still trying to reproduce that without any success, but I > get other kinds of failures which I think you'd be seeing too if that > hunch were right. Still looking...
Thanks for investigating! We have monitoring in place and a plan to grab stack traces if this happens again. Is there anything else that would be useful for us to try to get in addition to a stack trace from the process processing the stuck query?
