Re: There's some sort of race condition with the new FSM stuff

Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> The bug only affected fsync/forget requests that are forwarded from
> backends, not the ones that bgwriter puts into the hash table itself.

Oh, of course. So the actual sequence of events was:

* bgwriter queues an fsync request for a FSM fork, after
writing a dirty FSM buffer.
* backend drops table, sends forget request for FSM fork,
which the bug converts into an extra forget for the main fork.
* at checkpoint, we got trouble.

> I noted that kudu has a small shared_buffers setting, 5.6 MB, compared to
> most buildfarm members, which might explain different behavior wrt.
> which buffers are written by backends and which are written by bgwriter.

Yup, that must have been the determining factor. That would also
explain a certain amount of nondeterminism in the bug's manifestation,
which also squares with the buildfarm observations.

Okay, I feel better now.

regards, tom lane