Re: Ideas for a relcache test mode about missing invalidations

From: Andres Freund <andres(at)anarazel(dot)de>
To: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Ideas for a relcache test mode about missing invalidations
Date: 2018-08-02 16:03:09
Message-ID: 20180802160309.d7wuh3nmhsuxe5sj@alap3.anarazel.de
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Hi,

On 2018-08-02 19:18:11 +0900, Kyotaro HORIGUCHI wrote:
> At Wed, 1 Aug 2018 09:25:18 -0700, Andres Freund <andres(at)anarazel(dot)de> wrote in <20180801162518(dot)jnb2ql5dfmgwp4qo(at)alap3(dot)anarazel(dot)de>
> > Hi,
> >
> > The issue at [1] is caused by missing invalidations, and [2] seems like
> > a likely candidate too. I wonder if it'd be good to have a relcache test
> > mode akin to CLOBBER_CACHE_ALWAYS and RELCACHE_FORCE_RELEASE, that tries
> > to ensure that we've done sufficiently to ensure the right invalidations
> > are sent.
> >
> > I think what we'd kind of want is to ensure that relcache entries are
> > rebuilt at the earliest possible time, but *not* later. That'd mean
> > they're out of date if there's missing invalidations. Unfortunately I'm
> > not clear on how that'd be achievable? Ideas?
> >
> > The best I can come up with is to code some additional dependencies into
> > CacheInvalidateHeapTuple(), and add tracking ensuring we've sent the
> > right messages. But that seems somewhat painful and filled with holes.
> >
> > [1] http://archives.postgresql.org/message-id/CAKoxK%2B5fVodiCtMsXKV_1YAKXbzwSfp7DgDqUmcUAzeAhf%3DHEQ%40mail.gmail.com
> > [2] https://www.postgresql.org/message-id/12259.1532117714@sss.pgh.pa.us
>
> As for [1], it is not a issue on invalidation. It happens also if
> the relation has any index and even drop is not needed. The
> following steps are sufficient.

Huh? I don't think this is a proper fix. But please let's argue over in
the other that in the other thread.

Greetings,

Andres Freund

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