Re: BUG #18996: Assertion fails in waiteventset.c when dropping database in single mode in PG18

Patrick Stählin <me@packi.ch>

From: Patrick Stählin <me@packi.ch>

To: pgsql-bugs@lists.postgresql.org

Cc: Heikki Linnakangas <heikki.linnakangas@iki.fi>

Date: 2025-07-24T13:46:12Z

Lists: pgsql-bugs

Commits

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Fix assertion failure with latch wait in single-user mode
- f7dfccf9605d 18.0 landed
- 641f20d4c433 19 (unreleased) landed
Use ModifyWaitEvent to update exit_on_postmaster_death
- 84e5b2f07a5e 18.0 cited

Attachments

0001-Do-not-modify-wait-events-we-never-added.patch (text/x-patch) patch 0001

Hi!

On 7/24/25 11:49 AM, PG Bug reporting form wrote:
> 
> We're starting to incorporate PG18 (REL_18_BETA2) in our builds/testing. Our
> tests currently fail because we drop the postgres database in single mode
> before we give our customers access to them, as they won't have superuser
> access and we allow them to re-create that database. It also triggers when I
> create a database foo and then drop it so it's not related to the postgres
> database specifically. The assert doesn't trigger with REL_17_5 built with
> the same instructions.

We, or rather git bisect, traced it down to commit 
84e5b2f07a5e8ba983ff0f6e71b063b27f45f346 that added a new wait event in 
InitializeLatchWaitSet if we're running under postmaster but then didn't 
add the same check in WaitLatch and always referenced it. This probably 
caused the assert later on, when we were waiting on the ProcBarrier.

I've attached a patch based on REL_18_STABLE that seems to fix the issue 
for us and passes the selftests.

Thanks,
Patrick