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/utils/misc/guc_tables.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) (limited to 'src/backend/utils/misc/guc_tables.c') diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c index 60a40ed445a..ead80257192 100644 --- a/src/backend/utils/misc/guc_tables.c +++ b/src/backend/utils/misc/guc_tables.c @@ -3252,6 +3252,20 @@ struct config_int ConfigureNamesInt[] = NULL }, + { + {"io_max_combine_limit", + PGC_POSTMASTER, + RESOURCES_IO, + gettext_noop("Server-wide limit that clamps io_combine_limit."), + NULL, + GUC_UNIT_BLOCKS + }, + &io_max_combine_limit, + DEFAULT_IO_COMBINE_LIMIT, + 1, MAX_IO_COMBINE_LIMIT, + NULL, assign_io_max_combine_limit, NULL + }, + { {"io_combine_limit", PGC_USERSET, @@ -3263,7 +3277,7 @@ struct config_int ConfigureNamesInt[] = &io_combine_limit, DEFAULT_IO_COMBINE_LIMIT, 1, MAX_IO_COMBINE_LIMIT, - NULL, NULL, NULL + NULL, assign_io_combine_limit, NULL }, { -- cgit v1.2.3