From 10f6646847515b1ab02735c24b04abaf1996f65f Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Wed, 19 Mar 2025 11:40:56 +1300 Subject: 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 (earlier version) Discussion: https://postgr.es/m/CA%2BhUKG%2B2T9p-%2BzM6Eeou-RAJjTML6eit1qn26f9twznX59qtCA%40mail.gmail.com --- src/backend/commands/variable.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'src/backend/commands/variable.c') diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c index 4ad6e236d69..f550a3c0c63 100644 --- a/src/backend/commands/variable.c +++ b/src/backend/commands/variable.c @@ -1156,6 +1156,24 @@ assign_maintenance_io_concurrency(int newval, void *extra) #endif } +/* + * GUC assign hooks that recompute io_combine_limit whenever + * io_combine_limit_guc and io_max_combine_limit are changed. These are needed + * because the GUC subsystem doesn't support dependencies between GUCs, and + * they may be assigned in either order. + */ +void +assign_io_max_combine_limit(int newval, void *extra) +{ + io_max_combine_limit = newval; + io_combine_limit = Min(io_max_combine_limit, io_combine_limit_guc); +} +void +assign_io_combine_limit(int newval, void *extra) +{ + io_combine_limit_guc = newval; + io_combine_limit = Min(io_max_combine_limit, io_combine_limit_guc); +} /* * These show hooks just exist because we want to show the values in octal. -- cgit v1.2.3