Re: [HACKERS] Block level parallel vacuum

From: Mahendra Singh Thalor <mahi6run(at)gmail(dot)com>
To: Sergei Kornilov <sk(at)zsrv(dot)org>
Cc: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Amit Langote <langote_amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, David Steele <david(at)pgmasters(dot)net>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Block level parallel vacuum
Date: 2020-01-10 11:54:44
Message-ID: CAKYtNAroXD9C5bAiqne1KZV0vpEhfKZqbinH4AW9pDV_V9KYgQ@mail.gmail.com
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On Fri, 10 Jan 2020 at 15:51, Sergei Kornilov <sk(at)zsrv(dot)org> wrote:
>
> Hi
> Thank you for update! I looked again
>
> (vacuum_indexes_leader)
> + /* Skip the indexes that can be processed by parallel workers */
> + if (!skip_index)
> + continue;
>
> Does the variable name skip_index not confuse here? Maybe rename to something like can_parallel?

I also agree with your point.

>
> Another question about behavior on temporary tables. Use case: the user commands just "vacuum;" to vacuum entire database (and has enough maintenance workers). Vacuum starts fine in parallel, but on first temporary table we hit:
>
> + if (RelationUsesLocalBuffers(onerel) && params->nworkers >= 0)
> + {
> + ereport(WARNING,
> + (errmsg("disabling parallel option of vacuum on \"%s\" --- cannot vacuum temporary tables in parallel",
> + RelationGetRelationName(onerel))));
> + params->nworkers = -1;
> + }
>
> And therefore we turn off the parallel vacuum for the remaining tables... Can we improve this case?

Good point.
Yes, we should improve this. I tried to fix this. Attaching a delta
patch that is fixing both the comments.

--
Thanks and Regards
Mahendra Singh Thalor
EnterpriseDB: http://www.enterprisedb.com

Attachment Content-Type Size
v44-0002-delta_Allow-vacuum-command-to-process-indexes-in-parallel.patch application/octet-stream 1.6 KB

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