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

28.12.2016 23:43, Claudio Freire:
> Attached v4 patches with the requested fixes.

Sorry for being late, but the tests took a lot of time.

create table t1 as select i, md5(random()::text) from generate_series(0,400000000) as i;
create index md5_idx ON  t1(md5);
update t1 set md5 = md5((random() * (100 + 500))::text);
vacuum;

Patched vacuum used 2.9Gb of memory and vacuumed the index in one pass,
while for old version it took three passes (1GB+1GB+0.9GB).
Vacuum duration results:

vanilla:
LOG: duration: 4359006.327 ms  statement: vacuum verbose t1;
patched:
LOG: duration: 3076827.378 ms  statement: vacuum verbose t1;

We can see 30% vacuum speedup. I should note that this case can be 
considered
as favorable to vanilla vacuum: the table is not that big, it has just 
one index
and disk used is a fast fusionIO. We can expect even more gain on slower 
disks.

Thank you again for the patch. Hope to see it in 10.0.

-- 
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company