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From: Dimitrios Apostolou <[email protected]>
To: Kashif Zeeshan <[email protected]>
Cc: Muhammad Imtiaz <[email protected]>
Cc: [email protected]
Subject: Re: pg_stat_io clarifications: background worker, writes and reads
Date: Tue, 21 May 2024 21:20:36 +0200 (CEST)
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAAPsdhd4tpC6jHmg0ED4rvBZcLTf3Qx+pgPxC3XTjtRZTbAjTQ@mail.gmail.com>
References: <[email protected]>
	<CANwR1OSB93AwAqNfwheCq6xA5KWfpJqh3BkuU0Ta-wPzVzZUYg@mail.gmail.com>
	<[email protected]>
	<CAAPsdhd4tpC6jHmg0ED4rvBZcLTf3Qx+pgPxC3XTjtRZTbAjTQ@mail.gmail.com>

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 <[email protected]> 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

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