Re: [HACKERS] Vacuum: allow usage of more than 1GB of work mem

From: Claudio Freire <klaussfreire(at)gmail(dot)com>
To: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
Cc: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Andres Freund <andres(at)anarazel(dot)de>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Anastasia Lubennikova <a(dot)lubennikova(at)postgrespro(dot)ru>, Anastasia Lubennikova <lubennikovaav(at)gmail(dot)com>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Vacuum: allow usage of more than 1GB of work mem
Date: 2018-02-06 13:41:22
Message-ID: CAGTBQpaufC0o8OikWd8=5biXcbYjT51mPLfmy22NUjX6kUED0A@mail.gmail.com
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On Tue, Feb 6, 2018 at 10:18 AM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
> On Tue, Feb 6, 2018 at 4:35 AM, Kyotaro HORIGUCHI
> <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>> It's starting to look like a timing effect indeed.
>>
>> It seems to be truncation skip, maybe caused by concurrent
>> autovacuum.
>
> Good point, I'll also disable autovacuum on vactst.
>
>> See lazy_truncate_heap() for details. Updates of
>> pg_stat_*_tables can be delayed so looking it also can fail. Even
>> though I haven't looked the patch closer, the "SELECT
>> pg_relation_size()" doesn't seem to give something meaningful
>> anyway.
>
> Maybe then "explain (analyze, buffers, costs off, timing off, summary
> off) select * from vactst" then.
>
> The point is to check that the relation's heap has 0 pages.

Attached rebased patches with those changes mentioned above, namely:

- vacuum test now creates vactst with autovacuum disabled for it
- vacuum test on its own parallel group
- use explain analyze instead of pg_relation_size to check the
relation is properly truncated

Attachment Content-Type Size
0003-Vacuum-free-dead-tuples-array-as-early-as-possible-v8.patch text/x-patch 5.5 KB
0001-Vacuum-allow-using-more-than-1GB-work-mem-v15.patch text/x-patch 25.6 KB

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