| From: | Ken Marshall <ktm(at)rice(dot)edu> |
|---|---|
| To: | Hannu Krosing <hannuk(at)google(dot)com> |
| Cc: | Tomas Vondra <tomas(at)vondra(dot)me>, 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: | 2026-08-06 14:50:42 |
| Message-ID: | anSfQumImev8kDKI@customer.dllstxx1.isp.starlink.com |
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| Lists: | pgsql-hackers |
On Thu, Aug 06, 2026 at 04:31:44PM +0200, Hannu Krosing wrote:
> On Thu, Aug 6, 2026 at 2:11 PM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
> >
> > The executive summary is that lz4/zstd perform about the same, but zstd
> > has a clearly better compression ratio. I withdraw my initial plan to
> > default to lz4, and I agree we should default to zstd. (By "default" I
> > mean that "on" would use that algorithm, but the GUC would still default
> > to 'off' as before. Maybe we should reconsinder that for PG20, though?)
>
> Do you have any ideas why recovery on Azure is 10-20% faster for lz4
> (and surprisingly also pglz) than for zstd ?
>
> ---
> Hannu
Hi,
I know that lz4 has much higher decompression speed but I have no idea
why it would also be faster for pglz. Do they actually use it or call
lz4 under the hood?
My two cents is that since cloud CPU is much more expensive than cloud
storage we should pick the option that minimizes it. In the application
that I used, it was mostly to pull historic data so the key performance
metric was rapid decompression speed. It was the difference between a
sub-second screen draw and not. I would tend to lz4 even with the better
compression ratio from zstd.
Regards,
Ken
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