Increase default maintenance_io_concurrency to 16

melanieplageman · melanieplageman · commit cc6be07ebde2 · 2025-03-18T09:08:10.000-04:00
Since its introduction in fc34b0d, 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. ff79b5b 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 9256822 and c3e775e, 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
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
@@ -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>
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
@@ -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)
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
@@ -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
