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From: andres@anarazel.de
To: Craig James <cjames@emolecules.com>
Cc: Merlin Moncure <mmoncure@gmail.com>
Cc: Joshua D. Drake <jd@commandprompt.com>
Cc: Graeme B. Bell <graeme.bell@nibio.no>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: Hmmm... why does CPU-intensive pl/pgsql code parallelise so badly when queries parallelise fine? Anyone else seen this?
Date: Thu, 9 Jul 2015 00:45:18 +0200
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On 2015-07-08 15:38:24 -0700, Craig James wrote:
> From my admittedly naive point of view, it's hard to see why any of this
> matters. I have functions that do purely CPU-intensive mathematical
> calculations ... you could imagine something like is_prime(N) that
> determines if N is a prime number. I have eight clients that connect to
> eight backends. Each client issues an SQL command like, "select
> is_prime(N)" where N is a simple number.

I mostly replied to Merlin's general point (additionally in the context of
plpgsql).

But I have a hard time seing that postgres would be the bottleneck for a
is_prime() function (or something with similar characteristics) that's
written in C where the average runtime is more than, say, a couple
thousand cyles.  I'd like to see a profile of that.

Andres


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  Subject: Re: Hmmm... why does CPU-intensive pl/pgsql code parallelise so badly when queries parallelise fine? Anyone else seen this?
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