Re: Parallel Seq Scan vs kernel read ahead
| От | Ranier Vilela |
|---|---|
| Тема | Re: Parallel Seq Scan vs kernel read ahead |
| Дата | |
| Msg-id | CAEudQApf+Q0kde4MVZJG6piJEezvDOc-g4uVMT2cTc8qzg9spg@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Parallel Seq Scan vs kernel read ahead (Thomas Munro <thomas.munro@gmail.com>) |
| Ответы |
Re: Parallel Seq Scan vs kernel read ahead
|
| Список | pgsql-hackers |
Em qua., 20 de mai. de 2020 às 18:49, Thomas Munro <thomas.munro@gmail.com> escreveu:
On Wed, May 20, 2020 at 11:03 PM Ranier Vilela <ranier.vf@gmail.com> wrote:
> Time: 47767,916 ms (00:47,768)
> Time: 32645,448 ms (00:32,645)
Just to make sure kernel caching isn't helping here, maybe try making
the table 2x or 4x bigger? My test was on a virtual machine with only
4GB RAM, so the table couldn't be entirely cached.
4x bigger.
Postgres defaults settings.
postgres=# create table t as select generate_series(1, 800000000)::int i;
SELECT 800000000
postgres=# \timing
Timing is on.
postgres=# set max_parallel_workers_per_gather = 0;
SET
Time: 8,622 ms
postgres=# select count(*) from t;
count
-----------
800000000
(1 row)
Time: 227238,445 ms (03:47,238)
postgres=# set max_parallel_workers_per_gather = 1;
SET
Time: 20,975 ms
postgres=# select count(*) from t;
count
-----------
800000000
(1 row)
Time: 138027,351 ms (02:18,027)
SELECT 800000000
postgres=# \timing
Timing is on.
postgres=# set max_parallel_workers_per_gather = 0;
SET
Time: 8,622 ms
postgres=# select count(*) from t;
count
-----------
800000000
(1 row)
Time: 227238,445 ms (03:47,238)
postgres=# set max_parallel_workers_per_gather = 1;
SET
Time: 20,975 ms
postgres=# select count(*) from t;
count
-----------
800000000
(1 row)
Time: 138027,351 ms (02:18,027)
Ranier Vilela
В списке pgsql-hackers по дате отправления: