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Increase default maintenance_io_concurrency to 16

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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
This commit is contained in:
Melanie Plageman 2025-03-18 09:08:10 -04:00
parent 796bdda484
commit cc6be07ebd
3 changed files with 6 additions and 6 deletions
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8
doc/src/sgml/config.sgml
View File

@ -2617,10 +2617,10 @@ include_dir 'conf.d'
for maintenance work that is done on behalf of many client sessions.
</para>
<para>
The default is 10 on supported systems, otherwise 0. This value can
be overridden for tables in a particular tablespace by setting the
tablespace parameter of the same name (see
<xref linkend="sql-altertablespace"/>).
The default is <literal>16</literal> on supported systems, otherwise
<literal>0</literal>. This value can be overridden for tables in a
particular tablespace by setting the tablespace parameter of the same
name (see <xref linkend="sql-altertablespace"/>).
</para>
</listitem>
</varlistentry>

2
src/backend/utils/misc/postgresql.conf.sample
View File

@ -199,7 +199,7 @@
#backend_flush_after = 0 # measured in pages, 0 disables
#effective_io_concurrency = 16 # 1-1000; 0 disables prefetching
#maintenance_io_concurrency = 10 # 1-1000; 0 disables prefetching
#maintenance_io_concurrency = 16 # 1-1000; 0 disables prefetching
#io_combine_limit = 128kB # usually 1-32 blocks (depends on OS)
#io_method = sync # sync (change requires restart)

2
src/include/storage/bufmgr.h
View File

@ -153,7 +153,7 @@ extern PGDLLIMPORT bool track_io_timing;
/* only applicable when prefetching is available */
#ifdef USE_PREFETCH
#define DEFAULT_EFFECTIVE_IO_CONCURRENCY 16
#define DEFAULT_MAINTENANCE_IO_CONCURRENCY 10
#define DEFAULT_MAINTENANCE_IO_CONCURRENCY 16
#else
#define DEFAULT_EFFECTIVE_IO_CONCURRENCY 0
#define DEFAULT_MAINTENANCE_IO_CONCURRENCY 0