php-doc-en/reference/mysqlnd_ms/setup.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ --> 

<chapter xml:id="mysqlnd-ms.setup" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 &reftitle.setup;

 <section xml:id="mysqlnd-ms.requirements">
  &reftitle.required;
  <para>
    <literal>PHP 5.3.6</literal> or newer.
  </para>
  <para>
   The <literal>mysqlnd_ms</literal> replication and load balancing
   plugin supports all PHP applications and all availablePHP MySQL extensions 
   (<link linkend="ref.mysqli">mysqli</link>,
   <link linkend="ref.mysql">mysql</link>,
   <link linkend="ref.pdo-mysql">PDO_MYSQL</link>).
   The PHP MySQL extension must be configured to use
   <link linkend="book.mysqlnd">mysqlnd</link>  in order to be able
   to use the <literal>mysqlnd_ms</literal> plugin for
   <link linkend="book.mysqlnd">mysqlnd</link>.
  </para>
 </section>

 &reference.mysqlnd-ms.configure;
 &reference.mysqlnd-ms.ini;

 <section xml:id="mysqlnd-ms.plugin-ini">
  <title xmlns="http://docbook.org/ns/docbook">Plugin configuration file</title>
  <para>
   The plugin is using its own configuration file. The configuration file
   holds information on the MySQL replication master server,
   the MySQL replication slave servers, the server pick (load balancing) policy,
   the failover strategy and the use of lazy connections.
  </para>
  <para>
   The PHP configuration directive 
   <link linkend="ini.mysqlnd-ms.ini-file"><literal>mysqlnd_ms.ini_file</literal></link> 
   is used to set the plugins configuration file.
  </para>
  <para>
   The configuration file minics standard <literal>php.ini</literal> format.
   It consists of one or more sections. Every section defines its own unit
   of settings. There is no global section for setting defaults.
  </para>
  <para>
   Applications reference sections by their name. Applications use section names
   as the host (server) parameter to the various connect methods of the
   <link linkend="ref.mysqli">mysqli</link>,
   <link linkend="ref.mysql">mysql</link> and
   <link linkend="ref.pdo-mysql">PDO_MYSQL</link> extensions. Upon connect
   the <link linkend="book.mysqlnd">mysqlnd</link> plugin compares the hostname
   with all section names from the plugin configuration file. If hostname and
   section name match, the plugin will load the sections settings.
  </para>
  <para>
   <example>
    <title>Using section names example</title>
    <programlisting role="ini">
<![CDATA[
[myapp]
master[] = localhost
slave[] = 192.168.2.27
slave[] = 192.168.2.28:3306
[localhost]
master[] = localhost:/tmp/mysql/mysql.sock
slave[] = 192.168.3.24:3305
slave[] = 192.168.3.65:3309
]]>
    </programlisting>
    <programlisting role="php">
<![CDATA[
<?php
/* All of the following connections will be load balanced */
$mysqli = new mysqli("myapp", "username", "password", "database");
$pdo = new PDO('mysql:host=myapp;dbname=database', 'username', 'password');
$mysql = mysql_connect("myapp", "username", "password");

$mysqli = new mysqli("localhost", "username", "password", "database");
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   Section names are strings. It is valid to use a section name such as
   <literal>192.168.2.1</literal>, <literal>127.0.0.1</literal> or
   <literal>localhost</literal>. If, for example, an application
   connects to <literal>localhost</literal> and a plugin
   configuration section <literal>[localhost]</literal> exists, the
   semantics of the connect operation are changed. The application will
   no longer only use the MySQL server running on the host
   <literal>localhost</literal> but the plugin will start to load balance
   MySQL queries following the rules from the <literal>[localhost]</literal>
   configuration section. This way you can load balance queries from
   an application without changing the applications source code.
  </para>
  <para>
   The <literal>master[]</literal>, <literal>slave[]</literal>
   and <literal>pick[]</literal> configuration directives use a list-like syntax.
   Configuration directives supporting list-like syntax may appear multiple
   times in a configuration section. The plugin maintains the order in
   which entries appear when interpreting them. For example,
   the below example shows two <literal>slave[]</literal> configuration
   directives in the configuration section <literal>[myapp]</literal>.
   If doing round-robin load balancing for read-only queries, the plugin
   will send the first read-only query to the MySQL server
   <literal>mysql_slave_1</literal> because it is the first in the list.
   The second read-only query will be send to the MySQL server
   <literal>mysql_slave_2</literal> because it is the second in the list.
   Configuration directives supporting list-like syntax result are ordered
   from top to bottom in accordance to their appearance within a configuration
   section.
  </para>
  <para>
   <example>
    <title>List-like syntax</title>
    <programlisting role="ini">
<![CDATA[
[myapp]
master[] = mysql_master_server
slave[] = mysql_slave_1
slave[] = mysql_slave_2
]]>
    </programlisting>
    </example>
  </para>
  <para>
   Here is a short explanation of the configuration directives that can be used.
  </para>
  <para>
  <variablelist>
   <varlistentry xml:id="ini.mysqlnd-ms-plugin-config.master">
     <term>
      <parameter>master[]</parameter>
      <type>string</type>
     </term>
     <listitem>
      <para>
       URI of a MySQL replication master server. The URI follows the syntax
       <literal>hostname[:port|unix_domain_socket]</literal>.
      </para>
      <para>
       The plugin supports using only one master server.
      </para>
      <para>
       Setting a master server is mandatory. The plugin will report a
       warning upon connect if the user has failed to provide a master
       server for a configuration section.
       The warning may read
       <literal>(mysqlnd_ms) Cannot find master section in config</literal>.
       Furthermore the plugin may set an error code for the connection handle such as
       <literal>HY000/2000 (CR_UNKNOWN_ERROR)</literal>. The corresponding error
       message depends on your language settings.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry xml:id="ini.mysqlnd-ms-plugin-config.slave">
    <term>
      <parameter>slave[]</parameter>
      <type>string</type>
     </term>
     <listitem>
      <para>
       URI of one or more MySQL replication slave servers. The URI follows the syntax
       <literal>hostname[:port|unix_domain_socket]</literal>.
      </para>
      <para>
       The plugin supports using one or more slave servers.
      </para>
      <para>
       Setting a slave server is mandatory. The plugin will report a
       warning upon connect if the user has failed to provide at least one slave
       server for a configuration section. The warning may read
       <literal>(mysqlnd_ms) Cannot find slaves section in config</literal>.
       Furthermore the plugin may set an error code for the connection handle such as
       <literal>HY000/2000 (CR_UNKNOWN_ERROR)</literal>. The corresponding error
       message depends on your language settings.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry xml:id="ini.mysqlnd-ms-plugin-config.pick">
     <term>
      <parameter>pick[]</parameter>
      <type>string</type>
     </term>
     <listitem>
      <para>
       Load balancing (server picking) policy. Supported policies:
       <literal>random</literal>, <literal>random_once</literal> (default),
       <literal>roundrobin</literal>, <literal>user</literal>.
      </para>
      <para>
       If no load balancing policy is set, the plugin will default to
       <literal>random_once</literal>. The <literal>random_once</literal>
       policy picks a random slave server when running the first read-only
       statement. The slave server will be used for all read-only 
       statements until the PHP script execution ends.
      </para>
     <para>
       The <literal>random</literal> policy will pick a random server whenever
       a read-only statement is to be executed. 
     </para>
     <para>
       If using 
       <literal>roundrobin</literal> the plugin iterates over the list of
       configured slave servers to pick a server for statement execution. 
       If the plugin reaches the end of the list, it wraps around to the beginning
       of the list and picks the first configured slave server.
      </para>
      <para>
       Setting more than one load balancing policy for a configuration
       section makes only sense in conjunction with <literal>user</literal>
       and <function>mysqlnd_ms_set_user_pick_server</function>. If the
       user defined callback fails to pick a server, the plugin falls
       back to the second configured load balancing policy.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry xml:id="ini.mysqlnd-ms-plugin-config.failover">
     <term>
      <parameter>failover</parameter>
      <type>string</type>
     </term>
     <listitem>
      <para>
       Failover policy. Supported policies:
       <literal>disabled</literal> (default), <literal>master</literal>.
      </para>
      <para>
       If no failover policy is set, the plugin will not do any
       automatic failover (<literal>failover=disabled</literal>). Whenever
       the plugin fails to connect a server it will emit a warning and 
       set the connections error code and message. Thereafter it is up to 
       the application to handle the error and, for example, resent the
       last statement to trigger the selection of another server.
      </para>
      <para>
       If using <literal>failover=master</literal> the plugin will implicitly
       failover to a slave, if available. Please check the 
       concepts documentation to learn about potential
       pitfalls and risks of using <literal>failover=master</literal>.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry xml:id="ini.mysqlnd-ms-plugin-config.lazy_connections">
     <term>
      <parameter>lazy_connections</parameter>
      <type>bool</type>
     </term>
     <listitem>
      <para>
       Controls the use of lazy connections. Lazy connections
       are connections which are not opened before the client sends the first
       connection. 
      </para>
      <para>
       It is strongly recommended to use lazy connections.
       Lazy connections help to keep the the number of open connections low.
       If you disable lazy connections and, for example, configure one MySQL 
       replication master server and two MySQL replication slaves, the 
       plugin will open three connections upon the first call to a 
       connect function although the application might use the master 
       connection only. 
      </para>
      <para>
       Lazy connections bare a risk if you make heavy use of actions
       which change the state of a connection. The plugin does not dispatch
       all state changing actions to all connections from the connection pool.
       The few dispatched actions are applied to already opened connections
       only. Lazy connections opened in the future are not affected. 
       If, for example, the connection character set is changed using a 
       PHP MySQL API call, the plugin will change the character set of all 
       currently opened connection. It will not remeber the character set 
       change to apply it on lazy connections opened in the future. As a
       result the internal connection pool would hold connections using
       different character sets. This is not desired. Remember that character
       sets are taken into account for escaping.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry xml:id="ini.mysqlnd-ms-plugin-config.master_on_write">
     <term>
      <parameter>master_on_write</parameter>
      <type>bool</type>
     </term>
     <listitem>
      <para>
       If set, the plugin will use the master server only after the
       first statement has been executed on the master. Applications
       can still send statements to the slaves using SQL hints to
       overrule the automatic decision.
      </para>
      <para>
       The setting may help with replication lag. If an application runs
       an <literal>INSERT</literal> the plugin will, by default, use the
       master to execute all following statements, including 
       <literal>SELECT</literal> statements. This helps to avoid problems 
       with reads from slaves which have not replicated the 
       <literal>INSERT</literal> yet.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry xml:id="ini.mysqlnd-ms-plugin-config.trx_stickiness">
     <term>
      <parameter>trx_stickiness</parameter>
      <type>string</type>
     </term>
     <listitem>
      <para>
       Transaction stickiness policy. Supported policies:
       <literal>disabled</literal> (default), <literal>master</literal>.
      </para>
      <para>
       Experimental feature.
      </para>
      <para>
       The setting requires 5.3.99 or newer. If used with PHP older than 5.3.99,
       the plugin will emit a warning like 
       <literal>(mysqlnd_ms) trx_stickiness strategy is not supported before PHP 5.3.99</literal>.
      </para>
      <para>
       If no transaction stickiness policy is set or, 
       if setting <literal>trx_stickiness=disabled</literal>, 
       the plugin is not transaction aware. Thus, the plugin may load balance
       connections and switch connections in the middle of a transaction.
       The plugin is not transaction safe. SQL hints must be used 
       avoid connection switches during a transaction.
      </para>
      <para>
       As of PHP 5.3.99 the mysqlnd library allows the plugin to monitor 
       the <literal>autocommit</literal> mode set by calls to the 
       libraries <literal>trx_autocommit()</literal> function. 
       If setting <literal>trx_stickiness=master</literal> and 
       <literal>autocommit</literal> gets disabled by a PHP MySQL extension
       invoking the <literal>mysqlnd</literal> library internal
       function call <literal>trx_autocommit()</literal>, the plugin is made
       aware of the begin of a transaction. Then, the plugin stops load balancing
       and directs all statements to the master server until 
       <literal>autocommit</literal> is enabled. Thus, no SQL hints are required.
      </para>
      <para>
       An example of a PHP MySQL API function calling the <literal>mysqlnd</literal> 
       library internal function call <literal>trx_autocommit()</literal> is 
       <function>mysqli_autocommit</function>.
      </para>
      <para>
       Although setting <literal>trx_stickiness=master</literal>, the plugin
       cannot be made aware of <literal>autocommit</literal> mode changes caused
       by SQL statements such as <literal>SET AUTOCOMMIT=0</literal>.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </section>

</chapter>

<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"~/.phpdoc/manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->