From: | Andres Freund <andres(at)anarazel(dot)de> |
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To: | Thom Brown <thom(at)linux(dot)com> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: SendRowDescriptionMessage() is slow for queries with a lot of columns |
Date: | 2017-09-15 18:23:11 |
Message-ID: | 20170915182311.n7ukfdudutqsjyxy@alap3.anarazel.de |
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Lists: | pgsql-hackers |
Hi Thom,
Thanks for taking a whack at this!
On 2017-09-15 12:16:22 +0100, Thom Brown wrote:
> I've run a fairly basic test with a table with 101 columns, selecting
> a single row from the table and I get the following results:
>
>
> Columns with 1-character names:
>
> master (80 jobs, 80 connections, 60 seconds):
FWIW, I don't think it's useful to test this with a lot of concurrency -
at that point you're likely saturating the machine with context switches
etc. unless you have a lot of cores. As this is isn't related to
concurrency I'd rather just check a single connection.
> transaction type: /tmp/test.sql
> scaling factor: 1
> query mode: simple
I think you'd need to use prepared statements / -M prepared to see
benefits - when parsing statements for every execution the bottleneck is
elsewhere (hello O(#available_columns * #selected_columns) in
colNameToVar()).
Greetings,
Andres Freund
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