Date: Tue, 18 Mar 2025 16:08:22 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Increase default maintenance_io_concurrency to 16
Message-ID: <Z9nStg5TJssYfg_b@momjian.us>
References: <E1tuWgZ-0035xZ-0x@gemulon.postgresql.org>
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This commit makes our default random_page_cost = 4 out of line with
these new settings (assumes modern SSD/NAS/SAN hardware) and more out of
line with reality.

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On Tue, Mar 18, 2025 at 01:08:47PM +0000, Melanie Plageman wrote:
> Increase default maintenance_io_concurrency to 16
> 
> Since its introduction in fc34b0d9de27a, the default
> maintenance_io_concurrency has been larger than the default
> effective_io_concurrency. maintenance_io_concurrency primarily
> controlled prefetching done on behalf of the whole system, for
> operations like recovery. Therefore it makes sense for it to have a
> value equal to or greater than effective_io_concurrency, which controls
> I/O concurrency for reading a relation in a bitmap heap scan.
> 
> ff79b5b2ab increased effective_io_concurrency to 16, so we'll increase
> maintenance_io_concurrency as well. For now, though, we'll keep the
> defaults of effective_io_concurrency and maintenance_io_concurrency
> equal to one another (16).
> 
> On fast, high IOPs systems, significantly higher values of
> maintenance_io_concurrency are observably beneficial [1]. However, such
> values would flood low IOPs systems and increase overall system I/O
> latency.
> 
> It is worth mentioning that since 9256822608f and c3e775e608f,
> maintenance_io_concurrency also controls the I/O concurrency of each
> vacuum worker. Since many autovacuum workers may be simultaneously
> issuing I/Os, we want to keep maintenance_io_concurrency appropriately
> conservative.
> 
> [1] https://postgr.es/m/c5d52837-6256-0556-ac8c-d6d3d558820a%40enterprisedb.com
> 
> Suggested-by: Jakub Wartak <jakub.wartak@enterprisedb.com>
> Discussion: https://postgr.es/m/CAKZiRmxdHQaU%2B2Zpe6d%3Dx%3D0vigJ1sfWwwVYLJAf%3Dud_wQ_VcUw%40mail.gmail.com
> 
> Branch
> ------
> master
> 
> Details
> -------
> https://git.postgresql.org/pg/commitdiff/cc6be07ebde2aef7cc0507f997f563ce77c00a00
> 
> Modified Files
> --------------
> doc/src/sgml/config.sgml                      | 8 ++++----
> src/backend/utils/misc/postgresql.conf.sample | 2 +-
> src/include/storage/bufmgr.h                  | 2 +-
> 3 files changed, 6 insertions(+), 6 deletions(-)
> 


-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Do not let urgent matters crowd out time for investment in the future.