Re: [HACKERS] Block level parallel vacuum

From: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
To: sawada(dot)mshk(at)gmail(dot)com
Cc: kommi(dot)haribabu(at)gmail(dot)com, amit(dot)kapila16(at)gmail(dot)com, michael(dot)paquier(at)gmail(dot)com, Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp, thomas(dot)munro(at)enterprisedb(dot)com, robertmhaas(at)gmail(dot)com, david(at)pgmasters(dot)net, klaussfreire(at)gmail(dot)com, simon(at)2ndquadrant(dot)com, pavan(dot)deolasee(at)gmail(dot)com, pgsql-hackers(at)postgresql(dot)org
Subject: Re: [HACKERS] Block level parallel vacuum
Date: 2019-03-19 10:29:33
Message-ID: 20190319.192933.151094524.horiguchi.kyotaro@lab.ntt.co.jp
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At Tue, 19 Mar 2019 17:51:32 +0900, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote in <CAD21AoCUZQmyXrwDw57ejoR-j1QrGqm_vrQKOkif_aJK4Gih6Q(at)mail(dot)gmail(dot)com>
> On Tue, Mar 19, 2019 at 10:39 AM Haribabu Kommi
> <kommi(dot)haribabu(at)gmail(dot)com> wrote:
> > The performance results are good. Do we want to add the recommended
> > size in the document for the parallel option? the parallel option for smaller
> > tables can lead to performance overhead.
> >
>
> Hmm, I don't think we can add the specific recommended size because
> the performance gain by parallel lazy vacuum depends on various things
> such as CPU cores, the number of indexes, shared buffer size, index
> types, HDD or SSD. I suppose that users who want to use this option
> have some sort of performance problem such as that vacuum takes a very
> long time. They would use it for relatively larger tables.

Agree that we have no recommended setting, but I strongly think that documentation on the downside or possible side effect of this feature is required for those who are to use the feature.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center

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