From fc34b0d9de27ab5ac2887da00b3892bdabd89e45 Mon Sep 17 00:00:00 2001
From: Thomas Munro <tmunro@postgresql.org>
Date: Mon, 16 Mar 2020 12:31:34 +1300
Subject: Introduce a maintenance_io_concurrency setting.

Introduce a GUC and a tablespace option to control I/O prefetching, much
like effective_io_concurrency, but for work that is done on behalf of
many client sessions.

Use the new setting in heapam.c instead of the hard-coded formula
effective_io_concurrency + 10 introduced by commit 558a9165e08.  Go with
a default value of 10 for now, because it's a round number pretty close
to the value used for that existing case.

Discussion: https://postgr.es/m/CA%2BhUKGJUw08dPs_3EUcdO6M90GnjofPYrWp4YSLaBkgYwS-AqA%40mail.gmail.com
---
 doc/src/sgml/config.sgml                | 20 ++++++++++++++++++++
 doc/src/sgml/ref/alter_tablespace.sgml  | 11 +++++++----
 doc/src/sgml/ref/create_tablespace.sgml | 11 +++++++----
 3 files changed, 34 insertions(+), 8 deletions(-)

(limited to 'doc/src')

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3cac340f323..672bf6f1ee7 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2229,6 +2229,26 @@ include_dir 'conf.d'
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-maintenance-io-concurrency" xreflabel="maintenance_io_concurrency">
+       <term><varname>maintenance_io_concurrency</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>maintenance_io_concurrency</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Similar to <varname>effective_io_concurrency</varname>, but used
+         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"/>).
+        </para>
+       </listitem>
+      </varlistentry>
+ 
       <varlistentry id="guc-max-worker-processes" xreflabel="max_worker_processes">
        <term><varname>max_worker_processes</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/alter_tablespace.sgml b/doc/src/sgml/ref/alter_tablespace.sgml
index acec33469f1..356fb9f93f3 100644
--- a/doc/src/sgml/ref/alter_tablespace.sgml
+++ b/doc/src/sgml/ref/alter_tablespace.sgml
@@ -84,13 +84,16 @@ ALTER TABLESPACE <replaceable>name</replaceable> RESET ( <replaceable class="par
      <para>
       A tablespace parameter to be set or reset.  Currently, the only
       available parameters are <varname>seq_page_cost</varname>,
-      <varname>random_page_cost</varname> and <varname>effective_io_concurrency</varname>.
-      Setting either value for a particular tablespace will override the
+      <varname>random_page_cost</varname>, <varname>effective_io_concurrency</varname>
+      and <varname>maintenance_io_concurrency</varname>.
+      Setting these values for a particular tablespace will override the
       planner's usual estimate of the cost of reading pages from tables in
-      that tablespace, as established by the configuration parameters of the
+      that tablespace, and the executor's prefetching behavior, as established
+      by the configuration parameters of the
       same name (see <xref linkend="guc-seq-page-cost"/>,
       <xref linkend="guc-random-page-cost"/>,
-      <xref linkend="guc-effective-io-concurrency"/>).  This may be useful if
+      <xref linkend="guc-effective-io-concurrency"/>,
+      <xref linkend="guc-maintenance-io-concurrency"/>).  This may be useful if
       one tablespace is located on a disk which is faster or slower than the
       remainder of the I/O subsystem.
      </para>
diff --git a/doc/src/sgml/ref/create_tablespace.sgml b/doc/src/sgml/ref/create_tablespace.sgml
index c621ec2c6bf..462b8831c27 100644
--- a/doc/src/sgml/ref/create_tablespace.sgml
+++ b/doc/src/sgml/ref/create_tablespace.sgml
@@ -106,13 +106,16 @@ CREATE TABLESPACE <replaceable class="parameter">tablespace_name</replaceable>
        <para>
         A tablespace parameter to be set or reset.  Currently, the only
         available parameters are <varname>seq_page_cost</varname>,
-        <varname>random_page_cost</varname> and <varname>effective_io_concurrency</varname>.
-        Setting either value for a particular tablespace will override the
+        <varname>random_page_cost</varname>, <varname>effective_io_concurrency</varname>
+        and <varname>maintenance_io_concurrency</varname>.
+        Setting these values for a particular tablespace will override the
         planner's usual estimate of the cost of reading pages from tables in
-        that tablespace, as established by the configuration parameters of the
+        that tablespace, and the executor's prefetching behavior, as established
+        by the configuration parameters of the
         same name (see <xref linkend="guc-seq-page-cost"/>,
         <xref linkend="guc-random-page-cost"/>,
-        <xref linkend="guc-effective-io-concurrency"/>).  This may be useful if
+        <xref linkend="guc-effective-io-concurrency"/>,
+        <xref linkend="guc-maintenance-io-concurrency"/>).  This may be useful if
         one tablespace is located on a disk which is faster or slower than the
         remainder of the I/O subsystem.
        </para>
-- 
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