Thread: wal_compression = on: what is the algorithm?

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/16/runtime-config-wal.html
Description:

In
https://www.postgresql.org/docs/16/runtime-config-wal.html#GUC-WAL-COMPRESSION,
the option "on" is not described:

“The supported methods are pglz, lz4 (if PostgreSQL was compiled with
--with-lz4) and zstd (if PostgreSQL was compiled with --with-zstd). The
default value is off. ”

"on" was an available option before PG 15, and still seen in some docs.
If I understand the code in src/backend/utils/misc/guc_tables.c, "on" is the
same as "pglz". So I suggest:

“The supported methods are pglz, lz4 (if PostgreSQL was compiled with
--with-lz4) and zstd (if PostgreSQL was compiled with --with-zstd). The
default value is off.  The value on is synonym of pglz.”

I didn't see this discussed in
https://www.postgresql.org/message-id/flat/3037310D-ECB7-4BF1-AF20-01C10BB33A33%40yandex-team.ru

On Fri, Nov 15, 2024 at 03:30:59PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/16/runtime-config-wal.html
> Description:
> 
> In
> https://www.postgresql.org/docs/16/runtime-config-wal.html#GUC-WAL-COMPRESSION,
> the option "on" is not described:
> 
> “The supported methods are pglz, lz4 (if PostgreSQL was compiled with
> --with-lz4) and zstd (if PostgreSQL was compiled with --with-zstd). The
> default value is off. ”
> 
> "on" was an available option before PG 15, and still seen in some docs.
> If I understand the code in src/backend/utils/misc/guc_tables.c, "on" is the
> same as "pglz". So I suggest:
> 
> “The supported methods are pglz, lz4 (if PostgreSQL was compiled with
> --with-lz4) and zstd (if PostgreSQL was compiled with --with-zstd). The
> default value is off.  The value on is synonym of pglz.”

I think we kept 'on' just for backward compatibility, so we don't
mention it in the docs anymore.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  When a patient asks the doctor, "Am I going to die?", he means 
  "Am I going to die soon?"