From: paul.dubois
Date: July 22 2010 11:25pm
Subject: svn commit - mysqldoc@docsrva: r21868 - in trunk: . refman-4.1 refman-5.0 refman-5.1 refman-5.5 refman-6.0
List-Archive: http://lists.mysql.com/commits/114179
Message-Id: <201007222325.o6MNP2fF002468@docsrva.mysql.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Author: paul
Date: 2010-07-23 01:25:01 +0200 (Fri, 23 Jul 2010)
New Revision: 21868

Log:
 r61521@frost:  paul | 2010-07-22 18:19:38 -0500
 join_buffer_size clarification (James)


Modified:
   trunk/refman-4.1/dba-mysqld-server-core.xml
   trunk/refman-5.0/dba-mysqld-server-core.xml
   trunk/refman-5.1/dba-mysqld-server-core.xml
   trunk/refman-5.5/dba-mysqld-server-core.xml
   trunk/refman-6.0/dba-mysqld-server-core.xml

Property changes on: trunk
___________________________________________________________________
Name: svk:merge
   - 07c7e7b4-24e3-4b51-89d0-6dc09fec6bec:/mysqldoc-local/mysqldoc/trunk:35498
07c7e7b4-24e3-4b51-89d0-6dc09fec6bec:/mysqldoc-local/trunk:40851
4767c598-dc10-0410-bea0-d01b485662eb:/mysqldoc-local/mysqldoc/trunk:43968
4767c598-dc10-0410-bea0-d01b485662eb:/mysqldoc-local/trunk:44480
7d8d2c4e-af1d-0410-ab9f-b038ce55645b:/mysqldoc-local/mysqldoc:61511
b5ec3a16-e900-0410-9ad2-d183a3acac99:/mysqldoc-local/mysqldoc/trunk:14218
bf112a9c-6c03-0410-a055-ad865cd57414:/mysqldoc-local/mysqldoc/trunk:39036
bf112a9c-6c03-0410-a055-ad865cd57414:/mysqldoc-local/trunk:39546
   + 07c7e7b4-24e3-4b51-89d0-6dc09fec6bec:/mysqldoc-local/mysqldoc/trunk:35498
07c7e7b4-24e3-4b51-89d0-6dc09fec6bec:/mysqldoc-local/trunk:40851
4767c598-dc10-0410-bea0-d01b485662eb:/mysqldoc-local/mysqldoc/trunk:43968
4767c598-dc10-0410-bea0-d01b485662eb:/mysqldoc-local/trunk:44480
7d8d2c4e-af1d-0410-ab9f-b038ce55645b:/mysqldoc-local/mysqldoc:61521
b5ec3a16-e900-0410-9ad2-d183a3acac99:/mysqldoc-local/mysqldoc/trunk:14218
bf112a9c-6c03-0410-a055-ad865cd57414:/mysqldoc-local/mysqldoc/trunk:39036
bf112a9c-6c03-0410-a055-ad865cd57414:/mysqldoc-local/trunk:39546


Modified: trunk/refman-4.1/dba-mysqld-server-core.xml
===================================================================
--- trunk/refman-4.1/dba-mysqld-server-core.xml	2010-07-22 20:32:41 UTC (rev 21867)
+++ trunk/refman-4.1/dba-mysqld-server-core.xml	2010-07-22 23:25:01 UTC (rev 21868)
Changed blocks: 1, Lines Added: 13, Lines Deleted: 5; 1872 bytes

@@ -4917,15 +4917,23 @@
         </para>
 
         <para>
-          The size of the buffer that is used for plain index scans,
-          range index scans, and joins that do not use indexes and thus
-          perform full table scans. Normally, the best way to get fast
-          joins is to add indexes. Increase the value of
+          The minimum size of the buffer that is used for plain index
+          scans, range index scans, and joins that do not use indexes
+          and thus perform full table scans. Normally, the best way to
+          get fast joins is to add indexes. Increase the value of
           <literal role="sysvar">join_buffer_size</literal> to get a
           faster full join when adding indexes is not possible. One join
           buffer is allocated for each full join between two tables. For
           a complex join between several tables for which indexes are
-          not used, multiple join buffers might be necessary.
+          not used, multiple join buffers might be necessary. There is
+          no gain from setting the buffer larger than required to hold
+          each matching row, and all joins allocate at least the minimum
+          size, so use caution in setting this variable to a large value
+          globally. It is better to keep the global setting small and
+          change to a larger setting only in sessions that are doing
+          large joins. Memory allocation time can cause substantial
+          performance drops if the global size is larger than needed by
+          most queries that use it.
         </para>
       </listitem>
 


Modified: trunk/refman-5.0/dba-mysqld-server-core.xml
===================================================================
--- trunk/refman-5.0/dba-mysqld-server-core.xml	2010-07-22 20:32:41 UTC (rev 21867)
+++ trunk/refman-5.0/dba-mysqld-server-core.xml	2010-07-22 23:25:01 UTC (rev 21868)
Changed blocks: 1, Lines Added: 13, Lines Deleted: 5; 1936 bytes

@@ -5409,15 +5409,23 @@
         <para condition="dynamic:optvar:item" role="5.0:mysqld:join_buffer_size"/>
 
         <para>
-          The size of the buffer that is used for plain index scans,
-          range index scans, and joins that do not use indexes and thus
-          perform full table scans. Normally, the best way to get fast
-          joins is to add indexes. Increase the value of
+          The minimum size of the buffer that is used for plain index
+          scans, range index scans, and joins that do not use indexes
+          and thus perform full table scans. Normally, the best way to
+          get fast joins is to add indexes. Increase the value of
           <literal role="sysvar">join_buffer_size</literal> to get a
           faster full join when adding indexes is not possible. One join
           buffer is allocated for each full join between two tables. For
           a complex join between several tables for which indexes are
-          not used, multiple join buffers might be necessary.
+          not used, multiple join buffers might be necessary. There is
+          no gain from setting the buffer larger than required to hold
+          each matching row, and all joins allocate at least the minimum
+          size, so use caution in setting this variable to a large value
+          globally. It is better to keep the global setting small and
+          change to a larger setting only in sessions that are doing
+          large joins. Memory allocation time can cause substantial
+          performance drops if the global size is larger than needed by
+          most queries that use it.
         </para>
 
         <para>


Modified: trunk/refman-5.1/dba-mysqld-server-core.xml
===================================================================
--- trunk/refman-5.1/dba-mysqld-server-core.xml	2010-07-22 20:32:41 UTC (rev 21867)
+++ trunk/refman-5.1/dba-mysqld-server-core.xml	2010-07-22 23:25:01 UTC (rev 21868)
Changed blocks: 1, Lines Added: 13, Lines Deleted: 5; 1936 bytes

@@ -6095,15 +6095,23 @@
         <para condition="dynamic:optvar:item" role="5.1:mysqld:join_buffer_size"/>
 
         <para>
-          The size of the buffer that is used for plain index scans,
-          range index scans, and joins that do not use indexes and thus
-          perform full table scans. Normally, the best way to get fast
-          joins is to add indexes. Increase the value of
+          The minimum size of the buffer that is used for plain index
+          scans, range index scans, and joins that do not use indexes
+          and thus perform full table scans. Normally, the best way to
+          get fast joins is to add indexes. Increase the value of
           <literal role="sysvar">join_buffer_size</literal> to get a
           faster full join when adding indexes is not possible. One join
           buffer is allocated for each full join between two tables. For
           a complex join between several tables for which indexes are
-          not used, multiple join buffers might be necessary.
+          not used, multiple join buffers might be necessary. There is
+          no gain from setting the buffer larger than required to hold
+          each matching row, and all joins allocate at least the minimum
+          size, so use caution in setting this variable to a large value
+          globally. It is better to keep the global setting small and
+          change to a larger setting only in sessions that are doing
+          large joins. Memory allocation time can cause substantial
+          performance drops if the global size is larger than needed by
+          most queries that use it.
         </para>
 
         <para>


Modified: trunk/refman-5.5/dba-mysqld-server-core.xml
===================================================================
--- trunk/refman-5.5/dba-mysqld-server-core.xml	2010-07-22 20:32:41 UTC (rev 21867)
+++ trunk/refman-5.5/dba-mysqld-server-core.xml	2010-07-22 23:25:01 UTC (rev 21868)
Changed blocks: 1, Lines Added: 13, Lines Deleted: 5; 1936 bytes

@@ -5960,15 +5960,23 @@
         <para condition="dynamic:optvar:item" role="5.5:mysqld:join_buffer_size"/>
 
         <para>
-          The size of the buffer that is used for plain index scans,
-          range index scans, and joins that do not use indexes and thus
-          perform full table scans. Normally, the best way to get fast
-          joins is to add indexes. Increase the value of
+          The minimum size of the buffer that is used for plain index
+          scans, range index scans, and joins that do not use indexes
+          and thus perform full table scans. Normally, the best way to
+          get fast joins is to add indexes. Increase the value of
           <literal role="sysvar">join_buffer_size</literal> to get a
           faster full join when adding indexes is not possible. One join
           buffer is allocated for each full join between two tables. For
           a complex join between several tables for which indexes are
-          not used, multiple join buffers might be necessary.
+          not used, multiple join buffers might be necessary. There is
+          no gain from setting the buffer larger than required to hold
+          each matching row, and all joins allocate at least the minimum
+          size, so use caution in setting this variable to a large value
+          globally. It is better to keep the global setting small and
+          change to a larger setting only in sessions that are doing
+          large joins. Memory allocation time can cause substantial
+          performance drops if the global size is larger than needed by
+          most queries that use it.
         </para>
 
         <para>


Modified: trunk/refman-6.0/dba-mysqld-server-core.xml
===================================================================
--- trunk/refman-6.0/dba-mysqld-server-core.xml	2010-07-22 20:32:41 UTC (rev 21867)
+++ trunk/refman-6.0/dba-mysqld-server-core.xml	2010-07-22 23:25:01 UTC (rev 21868)
Changed blocks: 1, Lines Added: 13, Lines Deleted: 5; 1936 bytes

@@ -6231,15 +6231,23 @@
         <para condition="dynamic:optvar:item" role="6.0:mysqld:join_buffer_size"/>
 
         <para>
-          The size of the buffer that is used for plain index scans,
-          range index scans, and joins that do not use indexes and thus
-          perform full table scans. Normally, the best way to get fast
-          joins is to add indexes. Increase the value of
+          The minimum size of the buffer that is used for plain index
+          scans, range index scans, and joins that do not use indexes
+          and thus perform full table scans. Normally, the best way to
+          get fast joins is to add indexes. Increase the value of
           <literal role="sysvar">join_buffer_size</literal> to get a
           faster full join when adding indexes is not possible. One join
           buffer is allocated for each full join between two tables. For
           a complex join between several tables for which indexes are
-          not used, multiple join buffers might be necessary.
+          not used, multiple join buffers might be necessary. There is
+          no gain from setting the buffer larger than required to hold
+          each matching row, and all joins allocate at least the minimum
+          size, so use caution in setting this variable to a large value
+          globally. It is better to keep the global setting small and
+          change to a larger setting only in sessions that are doing
+          large joins. Memory allocation time can cause substantial
+          performance drops if the global size is larger than needed by
+          most queries that use it.
         </para>
 
         <para>