From 05bb918126ff01559808e66a63eea2f2f6b832ce Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Sun, 31 Mar 2024 17:24:44 +1300 Subject: [PATCH v14 6/7] Increase PG_IOV_MAX for bigger io_combine_limit. PG_IOV_MAX, our clamped version of IOV_MAX, constrains io_combine_limit. Change the clamp from 32 up to 128 vectors so that we can set io_combine_limit up to 1MB instead of 256kB (assuming BLCKSZ == 8kB). These numbers are fairly arbitrary and it's not at all clear that it's a good idea to run with large numbers, but we might as well at least allow experimentation. This will also affect the size of the writes when initializing WAL segments, which will change from 256kB to 1MB (assuming BLCKSZ == 8kB). --- src/include/port/pg_iovec.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/src/include/port/pg_iovec.h b/src/include/port/pg_iovec.h index 7255c1bd911..5055ede2c8e 100644 --- a/src/include/port/pg_iovec.h +++ b/src/include/port/pg_iovec.h @@ -33,8 +33,11 @@ struct iovec #endif -/* Define a reasonable maximum that is safe to use on the stack. */ -#define PG_IOV_MAX Min(IOV_MAX, 32) +/* + * Define a reasonable maximum that is safe to use on the stack but also allows + * io_combine_limit to reach large sizes. + */ +#define PG_IOV_MAX Min(IOV_MAX, 128) /* * Like preadv(), but with a prefix to remind us of a side-effect: on Windows -- 2.44.0