| From: | Hannu Krosing <hannuk(at)google(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(at)vondra(dot)me> |
| Cc: | Andreas Karlsson <andreas(at)proxel(dot)se>, Christoph Berg <myon(at)debian(dot)org>, Andrey Borodin <x4mmm(at)yandex-team(dot)ru>, wenhui qiu <qiuwenhuifx(at)gmail(dot)com>, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, Andres Freund <andres(at)anarazel(dot)de>, Jelte Fennema-Nio <postgres(at)jeltef(dot)nl>, Michael Paquier <michael(at)paquier(dot)xyz>, Japin Li <japinli(at)hotmail(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, John Naylor <johncnaylorls(at)gmail(dot)com> |
| Subject: | Re: WAL compression setting after PostgreSQL LZ4 default change |
| Date: | 2026-08-04 07:03:47 |
| Message-ID: | CAMT0RQT2JKFmiEnVUzGex2nmgvoYCegVD_+71e17o1p0fyHx8Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Aug 3, 2026 at 10:36 PM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
>
> On 8/3/26 15:36, Hannu Krosing wrote:
> > For the CPU usage vs compression ratio discussion, please remember
> > that for both lz4 and zstd this depends on certain "compression
> > effort" flags, which we do not expose to customers (we claim we
> > already choose the best ones for them :) )
> >
>
> I'm not sure we really make such claims.
Yeah, I re-checked and all the claims I remembered were from mailing
list discussions, not official docs.
> AFAIK we simply use the default
> compression levels, specified by the lz4/zstd library, and assume the
> authors picked the right trade offs. I think that's sensible.
It's a bit more complicated than that - we use zstd level 1 while the
default for the zstd command-line utility is level 3
We should keep this in mind when running any manual compression tests.
My recollection from running some manual tests a year or two ago is
that on compression side there was a fair bit of overlap in speed
between lz4 and zstd when looking across many compression levels.
However, lz4 was a clear winner in decompression speeds, being 2-3
times faster than zstd.
----
Hannu Krosing
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