Re: pg_stat_io clarifications: background worker, writes and reads

Hi Kashif, just to clarify my question, are you saying that the I/O from
parallel workers is recorded into the "background worker" entry of
pg_stat_io?

Thanks,
Dimitris

On Wed, 15 May 2024, Kashif Zeeshan wrote:

> Hi
> parallel worker are used for parallel execution of the queries and you can find the help in the below link.
>
> https://www.postgresql.org/docs/current/how-parallel-query-works.html
>
> Its controlled by following parameters.
>
> max_worker_processes = 6
> max_parallel_workers_per_gather = 3
> max_parallel_workers = 6
> The limit of concurrent parallel workers for the whole cluster is max_parallel_workers, which must be ≤ max_worker_processes. The limit of parallel workers per query is max_parallel_workers_per_gather.
>
> Thanks
> Kashif Zeeshan
> Bitnine Global
>
> On Wed, May 15, 2024 at 5:59 PM Dimitrios Apostolou <jimis(at)gmx(dot)net> wrote:
> So what is this particular "background worker" I'm seeing, given that I
> have no replication or extensions?
>
> Searching the logs I found entries like the following:
>
> LOG:  background worker "parallel worker" (PID 93384) exited with exit code 1
>
> This got logged when I killed a simple SELECT query that took too long
> doing parallel seqscans. Could it be that the entry in pg_stat_io named
> "background worker" also includes the parallel workers from a SELECT
> query?
>
> Thanks,
> Dimitris