Hi, On 2022-08-17 11:15:28 +0530, Pavan Deolasee wrote: > I've a slightly modified version of test_shm_mq, that I changed to include > a shared fileset. The motivation to do that came because I hit an > assertion failure with PG15 while doing some development work on BDR and I > suspected it to be a PG15 bug.
> I notice that pgstat_shutdown_hook() is registered as a before-shmem-exit > callback. The callback is responsible for detaching from the pgstat shared > memory segment. But looks like other parts of the system still expect it to > be available during later stages of proc exit. > It's not clear to me if pgstat shutdown should happen later or code that > gets executed later in the cycle should not try to use pgstat. It's also > entirely possible that my usage of SharedFileSet is completely wrong. If > that's the case, please let me know the mistake in the usage. I don't think we have the infrastructure for a nice solution to this at the moment - we need a fairly large overhaul of process initialization / shutdown to handle these interdependencies nicely. We can't move pgstat shutdown into on_dsm callback because that's too late to allocate *new* dsm segments, which we might need to do while flushing out pending stats. See https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=fa91d4c91f28f4819dc54f93adbd413a685e366a for a way to avoid the problem. Greetings, Andres Freund
