Re: generic plans and "initial" pruning

On Sat, Feb 22, 2025 at 12:55 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Amit Langote <amitlangote09(at)gmail(dot)com> writes:
> > The short of it is that the cached-plan-inval test in the
> > delay_execution suite can never be made to work under
> > CLOBBER_CACHE_ALWAYS. The test assumes that locks on partitions for a
> > reused generic plan are not taken until InitPlan(). However, under
> > CLOBBER_CACHE_ALWAYS, generic plans are never reused, so the test's
> > assumption never holds.
>
> Ugh.
>
> > I see two possible ways to address this:
>
> > 1. Find a way to disable the cached-plan-inval test in
> > CLOBBER_CACHE_ALWAYS builds. However, I haven't found any other test
> > that does this.
>
> > 2. Remove the test altogether, though that might be too drastic.
>
> Well, you could force matters with "set debug_discard_caches = 0"
> within the test, but I think that's just a band-aid that would
> not make the test fully stable. The point of CLOBBER_CACHE_ALWAYS
> is to model random arrival of cache flush events, which is *always*
> a possibility due to background activity (autovacuum for instance).
>
> We do have a couple of other regression tests that rely on
> "set debug_discard_caches = 0", and I've not seen many buildfarm
> failures tracing to that, but I don't trust it a whole lot.
>
> How badly do you want to keep this test case? It seems fairly
> rickety to me, even without this particular concern.

Hmm, yeah, I have to admit that even if we address this specific
issue, the risk of this test failing again outweighs the likelihood of
it catching a real breakage in the deferred lock mechanism.

I'll remove the test for now.

--
Thanks, Amit Langote