From: | Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: postgres_fdw - make cached connection functions tests meaningful |
Date: | 2021-07-21 10:11:06 |
Message-ID: | CALj2ACXZsp21gYYNtPAP6DL=8-vbuNLLcOqv5_mTx4nqz7JRAg@mail.gmail.com |
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On Sat, Jul 17, 2021 at 9:37 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> writes:
> > On Thu, Jul 15, 2021 at 3:48 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> More generally, though, I am not sure that I believe the premise of
> >> this patch. AFAICS it's assuming that forcing debug_discard_caches
> >> off guarantees zero cache flushes, which it does not.
>
> > Can the setting debug_discard_caches = 0 still make extra
> > flushes/discards (not the regular cache flushes/discards that happen
> > because of alters or changes in the cached elements)? My understanding
> > was that debug_discard_caches = 0, disables all the extra flushes with
> > clobber cache builds. If my understanding wasn't right, isn't it good
> > to mention it somewhere in the documentation or in the source code?
>
> The reason for this mechanism is that cache flushes can be triggered
> at any time by sinval messages from other processes (e.g., background
> autovacuums). Setting debug_discard_caches allows us to exercise
> that possibility exhaustively and make sure that the code is proof
> against cache entries disappearing unexpectedly. Not setting
> debug_discard_caches doesn't mean that that can't happen, only that
> you can't predict when it will happen.
Thanks. I'm fine with dropping this patch, hence I marked the CF entry
as "rejected".
Regards,
Bharath Rupireddy.
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