Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)

okay, so I realized v35 had an issue where I wasn't counting strategy
evictions correctly. fixed in attached v36. This made me wonder if there
is actually a way to add a test for evictions (in strategy and shared
contexts) that is not flakey.

On Sun, Oct 23, 2022 at 6:48 PM Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com> wrote:
>
> On Thu, Oct 20, 2022 at 10:31 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > - "repossession" is a very unintuitive name for me. If we want something like
> > it, can't we just name it reuse_failed or such?
>
> +1, I think "repossessed" is awkward. I think "reuse_failed" works,
> but no strong opinions on an alternate name.

Also, re: repossessed, I can change it to reuse_failed but I do think it
is important to give users a way to distinguish between bulkread
rejections of dirty buffers and strategies failing to reuse buffers due
to concurrent pinning (since the reaction to these two scenarios would
likely be different).

If we added another column called something like "claim_failed" which
counts buffers which we failed to reuse because of concurrent pinning or
usage, we could recommend use of this column together with
"reuse_failed" to determine the cause of the failed reuses for a
bulkread. We could also use "claim_failed" in IOContext shared to
provide information on shared buffer contention.

- Melanie