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Increase default effective_io_concurrency to 16

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The default effective_io_concurrency has been 1 since it was introduced
in b7b8f0b609. Referencing the associated discussion [1], it
seems 1 was chosen as a conservative value that seemed unlikely to cause
regressions.

Experimentation on high latency cloud storage as well as fast, local
nvme storage (see Discussion link) shows that even slightly higher
values improve query timings substantially. 1 actually performs worse
than 0 [2]. With effective_io_concurrency 1, we are not prefetching
enough to avoid I/O stalls, but we are issuing extra syscalls.

The new default is 16, which should be more appropriate for common
hardware while still avoiding flooding low IOPs devices with I/O
requests.

[1] https://www.postgresql.org/message-id/flat/FDDBA24E-FF4D-4654-BA75-692B3BA71B97%40enterprisedb.com
[2] https://www.postgresql.org/message-id/CAAKRu_Zv08Cic%3DqdCfzrQabpEXGrd9Z9UOW5svEVkCM6%3DFXA9g%40mail.gmail.com

Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CAAKRu_Z%2BJa-mwXebOoOERMMUMvJeRhzTjad4dSThxG0JLXESxw%40mail.gmail.com
This commit is contained in:
Melanie Plageman
2025-03-12 15:56:59 -04:00
parent af717317a0
commit ff79b5b2ab
3 changed files with 18 additions and 24 deletions
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2
src/backend/utils/misc/postgresql.conf.sample
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@ -198,7 +198,7 @@
# - I/O -
#backend_flush_after = 0 # measured in pages, 0 disables
#effective_io_concurrency = 1 # 1-1000; 0 disables prefetching
#effective_io_concurrency = 16 # 1-1000; 0 disables prefetching
#maintenance_io_concurrency = 10 # 1-1000; 0 disables prefetching
#io_combine_limit = 128kB # usually 1-32 blocks (depends on OS)