Horton

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

Claudio Freire <klaussfreire@gmail.com>

View thread View on postgr.es
From: Claudio Freire <klaussfreire@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Masahiko Sawada <sawada.mshk@gmail.com>, Anastasia Lubennikova <a.lubennikova@postgrespro.ru>, Anastasia Lubennikova <lubennikovaav@gmail.com>, PostgreSQL-Dev <pgsql-hackers@postgresql.org>
Date: 2017-04-11T18:59:56Z
Lists: pgsql-hackers 
On Tue, Apr 11, 2017 at 3:53 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> 1TB / 8kB per page * 60 tuples/page * 20% * 6 bytes/tuple = 9216MB of
> maintenance_work_mem
>
> So we'll allocate 128MB+256MB+512MB+1GB+2GB+4GB which won't be quite
> enough so we'll allocate another 8GB, for a total of 16256MB, but more
> than three-quarters of that last allocation ends up being wasted.
> I've been told on this list before that doubling is the one true way
> of increasing the size of an allocated chunk of memory, but I'm still
> a bit unconvinced.

There you're wrong. The allocation is capped to 1GB, so wastage has an
upper bound of 1GB.

Commits

  1. Prefetch blocks during lazy vacuum's truncation scan

  2. Explain unaccounted for space in pgstattuple.