Feedback-ID: i0fe9450f:Fastmail
Date: Wed, 1 Jul 2026 08:45:17 +0900
From: Michael Paquier <michael@paquier.xyz>
To: wenhui qiu <qiuwenhuifx@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>,
	Japin Li <japinli@hotmail.com>,
	John Naylor <johncnaylorls@gmail.com>,
	Christoph Berg <myon@debian.org>
Subject: Re: WAL compression setting after PostgreSQL LZ4 default change
Message-ID: <akRVDdkH1ntCpTBv@paquier.xyz>
References: 
 <CAGjGUAL1b=Mwd1SCvLbo+fivEr9KDpFcu4jmqKCZXwT=6CiiGQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
	protocol="application/pgp-signature"; boundary="M0oSdtd3OzyQQxPR"
Content-Disposition: inline
In-Reply-To: 
 <CAGjGUAL1b=Mwd1SCvLbo+fivEr9KDpFcu4jmqKCZXwT=6CiiGQ@mail.gmail.com>
Archived-At: 
 <https://www.postgresql.org/message-id/akRVDdkH1ntCpTBv%40paquier.xyz>
Precedence: bulk


--M0oSdtd3OzyQQxPR
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Tue, Jun 30, 2026 at 06:25:09PM +0800, wenhui qiu wrote:
> The recent PostgreSQL commit changes the default TOAST compression to lz4
> when LZ4 support is available, based on the rationale that LZ4 is general=
ly
> more efficient than pglz in terms of CPU usage and compression
> ratio.  Given that, should we also consider changing the default
> compression method used by wal_compression =3D on from pglz to lz4?

"on" is just a backward-compatible value, so we could let it as-is.

> Currently, wal_compression =3D on still maps to pglz, while lz4 has to be
> selected explicitly with:
>=20
> wal_compression =3D lz4
> If LZ4 is now considered stable and preferable enough to become the defau=
lt
> for TOAST compression, it may be worth aligning WAL compression behavior =
as
> well, or at least discussing whether on should continue to imply pglz.

If I were switch the default, for me zstd goes first, lz4 is a close
second, and pglz is the last of its class.  The only reason why we
have not chosen zstd for TOAST is the fact that we don't support it
(trickier to add support for it as we have to preserve on-disk=20
compatibility for inline compressed TOAST entries).

In short, lz4 is available in many environments, but I'm also ready to
bet that zstd is equally available in these environments.
--
Michael

--M0oSdtd3OzyQQxPR
Content-Type: application/pgp-signature; name=signature.asc

-----BEGIN PGP SIGNATURE-----

iQIzBAEBCgAdFiEEG72nH6vTowiyblFKnvQgOdbyQH0FAmpEVQ0ACgkQnvQgOdby
QH1YRQ//ZAuvNftSD75PplBDvlRl8MKJ+Av+RanBp1aYkHGw3RhV+QnwOPc4TpPa
+112owCWGAIcPiRPvGmsRpe3rVxbdpTSjJcKwF+AX8puIyZD+2VmHpQjteYvn3jD
yOy8KlAJiy3DAfe1X/6r02pHjrm52qY6WCtguk4DWuMy9iJNGvjtCZTmH9MAzb0X
i159dn8ci3DviX7rf4KB/if/S9bFnTMebF7RUnm1taB76UznlYf4ztNliYMtTB6j
K8gJTqAEykY9Hp0gHvQWv1MBK679A++gc/aHyS8lcgwnSzrWCpiDor1E5Ri1tdqJ
Zt+WMvOrWqqYqvLtPVDkmZJVLeXJyk0ufJM8vDcE93Q2Jft0htpI2PSmqWH43azx
iJ6d0As3Z7G0UceA5d8W0HgHHJv8aJPmTIaOjSYxiCaa0qi0WDz+8v4a/V64ACNr
00Jotv7XkLtGa9MXNe7vt5yym6L9x4Egf3hlSLVv/2lbXOdmVS6oan2wO4KC6D9M
99p9S3DmNBkRiqYReKQkHdlsV54EoZ8NCFR3D3nrBBed6F2FJkV2SjWO9ack/VDZ
Mw9jt9u4BGQ0Z78qIZnq9NR37Ps1CKwrvHvpPxjR45U6KlAFu73uBJ1EmK3ZsFGt
KUYvXLdeL9U8xLqodR5SCJ8yNcyOhVjSM1l8F3tOvamncut5EiA=
=9FZs
-----END PGP SIGNATURE-----

--M0oSdtd3OzyQQxPR--