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 <and...@anarazel.de> (earlier version) Discussion: https://postgr.es/m/CA%2BhUKG%2B2T9p-%2BzM6Eeou-RAJjTML6eit1qn26f9twznX59qtCA%40mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/10f6646847515b1ab02735c24b04abaf1996f65f Modified Files -------------- doc/src/sgml/config.sgml | 23 ++++++++++++++++++++++- src/backend/commands/variable.c | 18 ++++++++++++++++++ src/backend/storage/aio/aio_init.c | 17 ++++++----------- src/backend/storage/buffer/bufmgr.c | 5 ++++- src/backend/utils/misc/guc_tables.c | 16 +++++++++++++++- src/backend/utils/misc/postgresql.conf.sample | 2 ++ src/include/storage/bufmgr.h | 4 +++- src/include/utils/guc_hooks.h | 2 ++ 8 files changed, 72 insertions(+), 15 deletions(-)
