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

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