Re: BUG #17257: (auto)vacuum hangs within lazy_scan_prune()

On Fri, Oct 29, 2021 at 6:30 AM Alexander Lakhin <exclusion(at)gmail(dot)com> wrote:
> I can propose the debugging patch to reproduce the issue that replaces
> the hang with the assert and modifies a pair of crash-causing test
> scripts to simplify the reproducing. (Sorry, I have no time now to prune
> down the scripts further as I have to leave for a week.)
>
> The reproducing script is:

I cannot reproduce this bug by following your steps, even when the
assertion is made to fail after only 5 retries (5 is still ludicrously
excessive, 100 might be overkill). And even when I don't use a debug
build (and make the assertion into an equivalent PANIC). I wonder why
that is. I didn't have much trouble following your similar repro for
bug #17255.

My immediate goal in trying to follow your reproducer was to determine
what effect (if any) the pending bugfix for #17255 [1] has on this
bug. It seems more than possible that this bug is in fact a different
manifestation of the same underlying problem we see in #17255. And so
that should be the next thing we check here.

[1] https://postgr.es/m/CAH2-WzkpG9KLQF5sYHaOO_dSVdOjM+dv=nTEn85oNfMUTk836Q@mail.gmail.com
--
Peter Geoghegan