Horton

Introduce io_max_combine_limit.

Thomas Munro <tmunro@postgresql.org>

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Commit: 10f6646847515b1ab02735c24b04abaf1996f65f
Author: Thomas Munro <tmunro@postgresql.org>
Date: 2025-03-19T02:23:54Z
Releases: 18.0 
Introduce io_max_combine_limit.

The existing io_combine_limit can be changed by users.  The new
io_max_combine_limit is fixed at server startup time, and functions as a
silent clamp on the user setting.  That in itself is probably quite
useful, but the primary motivation is:

aio_init.c allocates shared memory for all asynchronous IOs including
some per-block data, and we didn't want to waste memory you'd never used
by assuming they could be up to PG_IOV_MAX.  This commit already halves
the size of 'AioHandleIov' and 'AioHandleData'.  A follow-up commit can
now expand PG_IOV_MAX without affecting that.

Since our GUC system doesn't support dependencies or cross-checks
between GUCs, the user-settable one now assigns a "raw" value to
io_combine_limit_guc, and the lower of io_combine_limit_guc and
io_max_combine_limit is maintained in io_combine_limit.

Reviewed-by: Andres Freund <andres@anarazel.de> (earlier version)
Discussion: https://postgr.es/m/CA%2BhUKG%2B2T9p-%2BzM6Eeou-RAJjTML6eit1qn26f9twznX59qtCA%40mail.gmail.com

Files

PathChange+/−
doc/src/sgml/config.sgml modified +22 −1
src/backend/commands/variable.c modified +18 −0
src/backend/storage/aio/aio_init.c modified +6 −11
src/backend/storage/buffer/bufmgr.c modified +4 −1
src/backend/utils/misc/guc_tables.c modified +15 −1
src/backend/utils/misc/postgresql.conf.sample modified +2 −0
src/include/storage/bufmgr.h modified +3 −1
src/include/utils/guc_hooks.h modified +2 −0

Documentation touched

Discussion