Re: Ideas for a relcache test mode about missing invalidations

From: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
To: andres(at)anarazel(dot)de
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Ideas for a relcache test mode about missing invalidations
Date: 2018-08-03 08:30:38
Message-ID: 20180803.173038.24919054.horiguchi.kyotaro@lab.ntt.co.jp
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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 they're out of date if there's missing invalidations.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

FWIW, I revisit here.

Maybe stupid, but does it make sense that we always build a new
relcache entry in RelationIdGetRelation then "logically" compare
it with the entry found in relcache? I'm not sure how referece
count affects this, though..

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center

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