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Date: Mon, 14 Oct 2024 09:30:07 +0200
From: Marc SCHAEFER <alphanet-postgresql-general@alphanet.ch>
To: pgsql-general@lists.postgresql.org
Subject: Re: Naive question about multithreading/multicore
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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!