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help / color / mirror / Atom feedFrom: Marc SCHAEFER <[email protected]>
To: [email protected]
Subject: Re: Naive question about multithreading/multicore
Date: Mon, 14 Oct 2024 09:30:07 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+hUKG+bjgdh7APFCC_8cZKnMzeagYjiEqTp+qn2koafGmi1aQ@mail.gmail.com>
References: <[email protected]>
<CA+hUKG+bjgdh7APFCC_8cZKnMzeagYjiEqTp+qn2koafGmi1aQ@mail.gmail.com>
Hello,
On Sun, Oct 13, 2024 at 08:16:04AM +1300, Thomas Munro wrote:
> > template1=> SELECT COUNT(*) FROM pg_class a, pg_class b, pg_class c;
> >
> > I see only one 100% CPU PostgreSQL process.
>
> If you set set min_parallel_table_scan_size = 0 then it uses
Without it, it uses one CPU and takes about 8.5 s (count is 57512456).
With it, it is indeed parallel (multiple CPU used) and it takes about 6s.
As this is on a machine with slow disks, it is perfectly ok, I just
wanted to see the CPU parallelism in action.
Thank you!
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