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: 2018-02-07 14:36:54
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On Wed, Feb 7, 2018 at 12:50 AM, Kyotaro HORIGUCHI
<horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> Hello,
> At Tue, 6 Feb 2018 10:41:22 -0300, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote in <CAGTBQpaufC0o8OikWd8=5biXcbYjT51mPLfmy22NUjX6kUED0A(at)mail(dot)gmail(dot)com>
>> 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.
> Ah, sorry. I meant by the above that it gives unstable result
> with autovacuum. So pg_relation_size() is usable after you turned
> of autovacuum on the table.

You did mention stats could be delayed

>> > 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
> The problematic test was in the 0001..v14 patch. The new
> 0001..v15 is identical to v14 and instead 0003-v8 has additional
> part that edits the test and expects added by 0001 into the shape
> as above. It seems that you merged the fixup onto the wrong
> commit.
> And may we assume it correct that 0002 is missing in this
> patchset?

Sounds like I botched the rebase. Sorry about that.

Attached are corrected versions (1-v16 and 3-v9)

Attachment Content-Type Size
0001-Vacuum-allow-using-more-than-1GB-work-mem-v16.patch text/x-patch 27.1 KB
0003-Vacuum-free-dead-tuples-array-as-early-as-possible-v9.patch text/x-patch 2.7 KB

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