Re: [PATCH] Add zstd compression for TOAST using extended header format

Hello,

You may want to consider sending the patch to the pgsql-hackers mailing list.

Murtuza Zabuawala
enterprisedb.com <http://enterprisedb.com/>

> On 16 Dec 2025, at 12:46 AM, Dharin Shah <dharinshah95(at)gmail(dot)com> wrote:
>
> Hello PG Hackers,
>
> Want to submit a patch that implements zstd compression for TOAST data using a 20-byte TOAST pointer format, directly addressing the concerns raised in prior discussions [1 <https://www.postgresql.org/message-id/flat/CAFAfj_F4qeRCNCYPk1vgH42fDZpjQWKO%2Bufq3FyoVyUa5AviFA%40mail.gmail.com#e41c78674adfa4d16b2fa82e59faf9aa>][2 <https://www.postgresql.org/message-id/flat/CAJ7c6TOtAB0z1UrksvGTStNE-herK-43bj22=5xVBg7S4vr5rQ(at)mail(dot)gmail(dot)com>][3 <https://www.postgresql.org/message-id/flat/YoMiNmkztrslDbNS(at)paquier(dot)xyz>].
>
> A bit of a background in the 2022 thread [3 <https://www.postgresql.org/message-id/flat/YoMiNmkztrslDbNS(at)paquier(dot)xyz>], The overall suggestion was to have something extensible for the TOAST header
>
> i.e. something like:
> 00 = PGLZ
> 01 = LZ4
> 10 = reserved for future emergencies
> 11 = extended header with additional type byte
>
> This patch implements that idea.
> The new header format:
>
> struct varatt_external_extended {
> int32 va_rawsize; /* same as legacy */
> uint32 va_extinfo; /* cmid=3 signals extended format */
> uint8 va_flags; /* feature flags */
> uint8 va_data[3]; /* va_data[0] = compression method */
> Oid va_valueid; /* same as legacy */
> Oid va_toastrelid; /* same as legacy */
> };
>
> A few notes:
>
> - Zstd only applies to external TOAST, not inline compression. The 2-bit limit in va_tcinfo stays as-is for inline data, where pglz/lz4 work fine anyway. Zstd's wins show up on larger values.
> - A GUC use_extended_toast_header controls whether pglz/lz4 also use the 20-byte format (defaults to off for compatibility, can enable it if you want consistency).
> - Legacy 16-byte pointers continue to work - we check the vartag to determine which format to read.
>
> The 4 extra bytes per pointer is negligible for typical TOAST data sizes, and it gives us room to grow.
>
> Regards,
> Dharin
> <zstd-toast-compression-external.patch>