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
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(-)
