Re: WAL compression setting after PostgreSQL LZ4 default change

On Wed, 01 Jul 2026 at 09:53, wenhui qiu <qiuwenhuifx@gmail.com> wrote:
> Hi Michael
>
>  > 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 
>  > 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.
>  Thanks for the feedback.
>
>  Yes, I did consider zstd as well. I agree that zstd can provide a better
>  compression ratio than lz4, and if we only look at compression ratio, zstd is
>  a very attractive choice.
>
>  The reason I started with lz4 was mainly to keep this change aligned with the
>  recent TOAST compression change. Since lz4 has already been accepted there as
>  the preferred default when available, I thought using the same choice for
>  wal_compression=on would make the proposal smaller, more consistent, and easier
>  to evaluate. so 
>
>  Second, WAL compression happens on the WAL insertion path for full-page images,
>  so compression speed and CPU overhead matter a lot. lz4 is generally a good fit
>  for that trade-off: it still reduces WAL volume, while keeping compression
>  latency and CPU cost lower than zstd in many workloads.
>
>  That said, I understand the argument for preferring zstd when it is available.
>  I have prepared an alternative version where wal_compression=on selects zstd
>  first, then lz4 if zstd is not available, and finally pglz as the fallback
>
> Thanks 

Thanks for updating the patch. I've registered it in the CommitFest [1].

[1] https://commitfest.postgresql.org/patch/6979/

-- 
Regards,
Japin Li
ChengDu WenWu Information Technology Co., Ltd.