Re: pglz compression performance, take two

> 9 дек. 2020 г., в 12:44, Andrey Borodin <x4mmm(at)yandex-team(dot)ru> написал(а):
> PFA the patch with some editorialisation by me.
> I saw some reports of bottlenecking in pglz WAL compression [1].

I've checked that on my machine simple test
echo "wal_compression = on" >> $PGDATA/postgresql.conf
pgbench -i -s 20 && pgbench -T 30
shows ~2-3% of improvement, but the result is not very stable, deviation is comparable. In fact, bottleneck is just shifted from pglz, thus impact is not that measurable.

I've found out that the patch continues ideas from thread [0] and commit 031cc55 [1], but in much more shotgun-surgery way.
Out of curiosity I've rerun tests from that thread
postgres=# with patched as (select testname, avg(seconds) patched from testresults0 group by testname),unpatched as (select testname, avg(seconds) unpatched from testresults group by testname) select * from unpatched join patched using (testname);
testname | unpatched | patched
-------------------+------------------------+------------------------
512b random | 4.5568015000000000 | 4.3512980000000000
100k random | 1.03342300000000000000 | 1.00326200000000000000
100k of same byte | 2.1689715000000000 | 2.0958155000000000
2k random | 3.1613815000000000 | 3.1861350000000000
512b text | 5.7233600000000000 | 5.3602330000000000
5k text | 1.7044835000000000 | 1.8086770000000000
(6 rows)

Results of direct call are somewhat more clear.
Unpatched:
testname | auto
-------------------+-----------
5k text | 1100.705
512b text | 240.585
2k random | 106.865
100k random | 2.663
512b random | 145.736
100k of same byte | 13426.880
(6 rows)

Patched:
testname | auto
-------------------+----------
5k text | 767.535
512b text | 159.076
2k random | 77.126
100k random | 1.698
512b random | 95.768
100k of same byte | 6035.159
(6 rows)

Thanks!

Best regards, Andrey Borodin.

[0] https://www.postgresql.org/message-id/flat/5130C914.8080106%40vmware.com
[1] https://github.com/x4m/postgres_g/commit/031cc55bbea6b3a6b67c700498a78fb1d4399476