Re: pglz performance

From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Andrey Borodin <x4mmm(at)yandex-team(dot)ru>, Gasper Zejn <zejn(at)owca(dot)info>, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: pglz performance
Date: 2019-11-01 16:59:50
Message-ID: 20191101165950.b5azncggaqfan5fi@development
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On Fri, Nov 01, 2019 at 12:48:28PM -0300, Alvaro Herrera wrote:
>On 2019-Nov-01, Peter Eisentraut wrote:
>> On 2019-10-25 07:05, Andrey Borodin wrote:
>> > > 21 окт. 2019 г., в 14:09, Andrey Borodin <x4mmm(at)yandex-team(dot)ru> написал(а):
>> > >
>> > > With Silesian corpus pglz_decompress_hacked is actually decreasing performance on high-entropy data.
>> > > Meanwhile pglz_decompress_hacked8 is still faster than usual pglz_decompress.
>> > > In spite of this benchmarks, I think that pglz_decompress_hacked8 is safer option.
>> >
>> > Here's v3 which takes into account recent benchmarks with Silesian Corpus and have better comments.
>> Your message from 21 October appears to say that this change makes the
>> performance worse. So I don't know how to proceed with this.
>As I understand that report, in these results "less is better", so the
>hacked8 variant shows better performance (33.8) than current (42.5).
>The "hacked" variant shows worse performance (48.2) that the current
>code. The "in spite" phrase seems to have been a mistake.
>I am surprised that there is so much variability in the performance
>numbers, though, based on such small tweaks of the code.

I'd try running the benchmarks to verify the numbers, and maybe do some
additional tests, but it's not clear to me which patches should I use.

I think the last patches with 'hacked' and 'hacked8' in the name are a
couple of months old, and the recent posts attach just a single patch.
Andrey, can you post current versions of both patches?


Tomas Vondra
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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