sigmasternchen/php-doc-en
1
0
Fork 0
mirror of https://github.com/sigmasternchen/php-doc-en synced 2025-03-25 05:18:56 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions
php-doc-en/reference/mysqlnd_ms/setup.xml
Philip Olson 04ed2d718d Fixed typos 
git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@327386 c90b9560-bf6c-de11-be94-00142212c4b1
2012-08-30 21:12:29 +00:00

2794 lines
101 KiB
XML
Executable file
Raw Blame History

<?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.
Some advanced functionality requires <literal>PHP 5.4.0</literal> or newer.
</para>
<para>
The <literal>mysqlnd_ms</literal> replication and load balancing
plugin supports all PHP applications and all available PHP 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-json">
<title xmlns="http://docbook.org/ns/docbook">Plugin configuration file (&gt;=1.1.x)</title>
<note>
<title>Changelog: Feature was added in PECL/mysqlnd_ms 1.1.0-beta</title>
<para>
The below description applies to PECL/mysqlnd_ms &gt;= 1.1.0-beta.
It is not valid for prior versions.
</para>
</note>
<para>
The plugin uses its own configuration file. The configuration file
holds information about 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 plugin loads its configuration file at the beginning of a web request.
It is then cached in memory and used for the duration of the web request.
This way, there is no need to restart PHP after deploying the configuration
file. Configuration file changes will become active almost instantly.
</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. Please note, that
the PHP configuration directive may not be evaluated for every web request.
Therefore, changing the plugins configuration file name or location may
require a PHP restart. However, no restart is required to read changes if
an already existing plugin configuration file is updated.
</para>
<para>
Using and parsing <acronym>JSON</acronym> is efficient, and using <acronym>JSON</acronym>
makes it easier to express hierarchical data structures than the standard
<filename>php.ini</filename> format.
</para>
<para>
<example>
<title>Converting a PHP array (hash) into JSON format</title>
<para>
Or alternatively, a developer may be more familiar with the PHP <type>array</type>
syntax, and prefer it. This example demonstrates how a developer might convert a
PHP array to <acronym>JSON</acronym>.
</para>
<programlisting role="php">
<![CDATA[
<?php
$config = array(
"myapp" => array(
"master" => array(
"master_0" => array(
"host" => "localhost",
"socket" => "/tmp/mysql.sock",
),
),
"slave" => array(),
),
);
file_put_contents("mysqlnd_ms.ini", json_encode($config, JSON_PRETTY_PRINT));
printf("mysqlnd_ms.ini file created...\n");
printf("Dumping file contents...\n");
printf("%s\n", str_repeat("-", 80));
echo file_get_contents("mysqlnd_ms.ini");
printf("\n%s\n", str_repeat("-", 80));
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
mysqlnd_ms.ini file created...
Dumping file contents...
--------------------------------------------------------------------------------
{
"myapp": {
"master": {
"master_0": {
"host": "localhost",
"socket": "\/tmp\/mysql.sock"
}
},
"slave": [
]
}
}
--------------------------------------------------------------------------------
]]>
</screen>
</example>
</para>
<para>
A plugin configuration file consists of one or more sections. Sections
are represented by the top-level object properties of the
object encoded in the <acronym>JSON</acronym> file. Sections could also
be called <emphasis>configuration names</emphasis>.
</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 of the section names from the plugin configuration file. If the hostname and
section name match, then the plugin will load the settings for that section.
</para>
<para xml:id="mysqlnd-ms.plugin-ini-json.using-section">
<example>
<title>Using section names example</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.2.27"
},
"slave_1": {
"host": "192.168.2.27",
"port": 3306
}
}
},
"localhost": {
"master": [
{
"host": "localhost",
"socket": "\/path\/to\/mysql.sock"
}
],
"slave": [
{
"host": "192.168.3.24",
"port": "3305"
},
{
"host": "192.168.3.65",
"port": "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.
Please keep in mind, that such a configuration may not contribute
to overall readability of your applications source code. Using section names
that can be mixed up with host names should be seen as a last resort.
</para>
<para xml:id="mysqlnd-ms.plugin-ini-json.server-list-syntax">
Each configuration section contains, at a minimum, a list of master servers
and a list of slave servers. The master list is configured with the keyword
<literal>master</literal>, while the slave list is configured with the
<literal>slave</literal> keyword. Failing to provide a slave list will result
in a fatal <constant>E_ERROR</constant> level error, although a slave list
may be empty. It is possible to allow no slaves. However, this is only recommended
with synchronous clusters, please see also
<link linkend="mysqlnd-ms.supportedclusters">supported clusters</link>.
The main part of the documentation focusses on the use
of asynchronous MySQL replication clusters.
</para>
<para>
The master and slave server lists can be optionally indexed by symbolic
names for the servers they describe. Alternatively, an array of descriptions
for slave and master servers may be used.
</para>
<para>
<example>
<title>List of anonymous slaves</title>
<programlisting role="ini">
<![CDATA[
"slave": [
{
"host": "192.168.3.24",
"port": "3305"
},
{
"host": "192.168.3.65",
"port": "3309"
}
]
]]>
</programlisting>
</example>
</para>
<para>
An anonymous server list is encoded by the <literal>JSON array</literal> type.
Optionally, symbolic names may be used for indexing the slave or master servers
of a server list, and done so using the <literal>JSON object</literal> type.
</para>
<para>
<example>
<title>Master list using symbolic names</title>
<programlisting role="ini">
<![CDATA[
"master": {
"master_0": {
"host": "localhost"
}
}
]]>
</programlisting>
</example>
</para>
<para>
It is recommended to index the server lists with symbolic server names.
The alias names will be shown in error messages.
</para>
<para>
The order of servers is preserved and taken into account by mysqlnd_ms.
If, for example, you configure round robin load balancing strategy, the
first <literal>SELECT</literal> statement will be executed on the
slave that appears first in the slave server list.
</para>
<para>
A configured server can be described with the <literal>host</literal>,
<literal>port</literal>, <literal>socket</literal>, <literal>db</literal>,
<literal>user</literal>, <literal>password</literal> and <literal>connect_flags</literal>.
It is mandatory to set the database server host using the <literal>host</literal>
keyword. All other settings are optional.
</para>
<para>
<example>
<title>Keywords to configure a server</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "db_server_host",
"port": "db_server_port",
"socket": "db_server_socket",
"db": "database_resp_schema",
"user": "user",
"password": "password",
"connect_flags": 0
}
},
"slave": {
"slave_0": {
"host": "db_server_host",
"port": "db_server_port",
"socket": "db_server_socket"
}
}
}
}
]]>
</programlisting>
</example>
</para>
<para>
If a setting is omitted, the plugin will use the value provided by the user
API call used to open a connection. Please, see the
<link linkend="mysqlnd-ms.plugin-ini-json.using-section">using section names example</link> above.
</para>
<para>
The configuration file format has been changed in version 1.1.0-beta to allow for
chained filters. Filters are responsible for filtering the configured list of
servers to identify a server for execution of a given statement.
Filters are configured with the <literal>filter</literal> keyword. Filters
are executed by mysqlnd_ms in the order of their appearance.
Defining filters is optional. A configuration section in the plugins
configuration file does not need to have a <literal>filters</literal> entry.
</para>
<para>
Filters replace the
<link linkend="ini.mysqlnd-ms-plugin-config.pick"><literal>pick[]</literal></link>
setting from prior versions. The new <literal>random</literal> and
<literal>roundrobin</literal> provide the same functionality.
</para>
<para>
<example>
<title>New <literal>roundrobin</literal> filter, old functionality</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
},
"slave_1": {
"host": "192.168.78.137",
"port": "3306"
}
},
"filters": {
"roundrobin": [
]
}
}
}
]]>
</programlisting>
</example>
</para>
<para>
The function
<function>mysqlnd_ms_set_user_pick_server</function>
has been removed. Setting a callback is now done with the <literal>user</literal>
filter. Some filters accept parameters. The <literal>user</literal> filter
requires and accepts a mandatory <literal>callback</literal> parameter
to set the callback previously set through the function <function>mysqlnd_ms_set_user_pick_server</function>.
<example>
<title>The <literal>user</literal> filter replaces <function>mysqlnd_ms_set_user_pick_server</function></title>
<programlisting role="ini">
<![CDATA[
"filters": {
"user": {
"callback": "pick_server"
}
}
]]>
</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-v2.master">
<term>
<parameter>master</parameter>
<type>array or object</type>
</term>
<listitem>
<para>
List of MySQL replication master servers. The list of either
of the <literal>JSON type array</literal> to declare an anonymous list
of servers or of the <literal>JSON type object</literal>. Please,
see <link linkend="mysqlnd-ms.plugin-ini-json.server-list-syntax">above</link>
for examples.
</para>
<para>
Setting at least one master server is mandatory. The plugin will issue an
error of type <literal>E_ERROR</literal> if the user has failed to
provide a master server list for a configuration section.
The fatal error may read
<literal>(mysqlnd_ms) Section [master] doesn't exist for host
[name_of_a_config_section] in %s on line %d</literal>.
</para>
<para>
A server is described with
the <literal>host</literal>, <literal>port</literal>,
<literal>socket</literal>, <literal>db</literal>,
<literal>user</literal>, <literal>password</literal> and
<literal>connect_flags</literal>. It is mandatory to
provide at a value for <literal>host</literal>. If any of the
other values is not given, it will be taken from the user
API connect call, please, see also:
<link linkend="mysqlnd-ms.plugin-ini-json.using-section">using section names example</link>.
</para>
<para xml:id="mysqlnd-ms.plugin-ini-json.server-config-keywords">
Table of server configuration keywords.
</para>
<informaltable>
<tgroup cols="3">
<colspec colwidth="1*"/>
<colspec colwidth="7*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Keyword</entry>
<entry>Description</entry>
<entry>Version</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>host</literal>
</entry>
<entry>
<para>
Database server host. This is a mandatory setting.
Failing to provide, will cause an error of type <literal>E_RECOVERABLE_ERROR</literal>
when the plugin tries to connect to the server. The error message may
read <literal>(mysqlnd_ms) Cannot find [host] in
[%s] section in config in %s on line %d</literal>.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>port</literal>
</entry>
<entry>
<para>
Database server TCP/IP port.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>socket</literal>
</entry>
<entry>
<para>
Database server Unix domain socket.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>db</literal>
</entry>
<entry>
<para>
Database (schemata).
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>user</literal>
</entry>
<entry>
<para>
MySQL database user.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>password</literal>
</entry>
<entry>
<para>
MySQL database user password.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>connect_flags</literal>
</entry>
<entry>
<para>
Connection flags.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The plugin supports using only one master server. An experimental
setting exists to enable multi-master support. The details are
not documented. The setting is meant for development only.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.slave">
<term>
<parameter>slave</parameter>
<type>array or object</type>
</term>
<listitem>
<para>
List of one or more MySQL replication slave servers. The syntax is
identical to setting master servers, please, see
<link linkend="ini.mysqlnd-ms-plugin-config-v2.master"><literal>master</literal></link>
above for details.
</para>
<para>
The plugin supports using one or more slave servers.
</para>
<para>
Setting a list of slave servers is mandatory. The plugin will report
an error of the type <literal>E_ERROR</literal> if <literal>slave</literal>
is not given for a configuration section. The fatal error message may read
<literal>(mysqlnd_ms) Section [slave] doesn't exist for host [%s] in %s on line %d</literal>.
Note, that it is valid to use an empty slave server list.
The error has been introduced to prevent accidently setting no slaves by
forgetting about the <literal>slave</literal> setting.
A master-only setup is still possible using an empty slave server list.
</para>
<para>
If an empty slave list is configured and an attempt is made to
execute a statement on a slave the plugin may emit a warning like
<literal>mysqlnd_ms) Couldn't find the appropriate slave connection.
0 slaves to choose from.</literal> upon statement execution.
It is possible that another warning follows such as
<literal>(mysqlnd_ms) No connection selected by the last filter</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.gtid">
<term>
<parameter>global_transaction_id_injection</parameter>
<type>array or object</type>
</term>
<listitem>
<para>
Global transaction identifier configuration related to both
the use of the server built-in global transaction ID feature and
the client-side emulation.
</para>
<informaltable>
<tgroup cols="3">
<colspec colwidth="1*"/>
<colspec colwidth="7*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Keyword</entry>
<entry>Description</entry>
<entry>Version</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>fetch_last_gtid</literal>
</entry>
<entry>
<para>
SQL statement for accessing the latest global transaction identifier.
The SQL statement is run if the plugin needs to know the most recent
global transaction identifier. This can be the case, for example, when checking
MySQL Replication slave status.
Also used with <function>mysqlnd_ms_get_last_gtid</function>.
</para>
</entry>
<entry>Since 1.2.0.</entry>
</row>
<row>
<entry>
<literal>check_for_gtid</literal>
</entry>
<entry>
<para>
SQL statement for checking if a replica has replicated
all transactions up to and including ones searched for. The
SQL statement is run when searching for replicas which can offer
a higher level of consistency than eventual consistency.
The statement must contain a placeholder <literal>#GTID</literal>
which is to be replaced with the global transaction identifier searched
for by the plugin. Please, check the
<link linkend="mysqlnd-ms.quickstart.gtid">quickstart</link> for examples.
</para>
</entry>
<entry>Since 1.2.0.</entry>
</row>
<row>
<entry>
<literal>report_errors</literal>
</entry>
<entry>
<para>
Whether to emit an error of type warning if an issue occurs while
executing any of the configured SQL statements.
</para>
</entry>
<entry>Since 1.2.0.</entry>
</row>
<row>
<entry>
<literal>on_commit</literal>
</entry>
<entry>
<para>
Client-side global transaction ID emulation only. SQL statement
to run when a transaction finished to update the global transaction
identifier sequence number on the master. Please, see the
<link linkend="mysqlnd-ms.quickstart.gtid">quickstart</link> for examples.
</para>
</entry>
<entry>Since 1.2.0.</entry>
</row>
<row>
<entry>
<literal>wait_for_gtid_timeout</literal>
</entry>
<entry>
<para>
Instructs the plugin to wait up to <literal>wait_for_gtid_timeout</literal>
seconds for a slave to catch up when searching for slaves that can
deliver session consistency. The setting limits the time spend for
polling the slave status. If polling the status takes very long, the total
clock time spend waiting may exceed <literal>wait_for_gtid_timeout</literal>.
The plugin calls <literal>sleep(1)</literal> to sleep one second between
each two polls.
</para>
<para>
The setting can be used both with the plugins client-side emulation
and the server-side global transaction identifier feature of MySQL 5.6.
</para>
<para>
Waiting for a slave to replicate a certain GTID needed for session
consistency also means throttling the client. By throttling the
client the write load on the master is reduced indirectly. A
primary copy based replication system, such as MySQL Replication,
is given more time to reach a consistent state. This can be desired,
for example, to increase the number of data copies for
high availability considerations or to prevent the master from being
overloaded.
</para>
</entry>
<entry>Since 1.4.0.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.filters">
<term>
<parameter>filters</parameter>
<type>object</type>
</term>
<listitem>
<para>
List of filters. A filter is responsible to filter the list of available
servers for executing a given statement. Filters can be chained.
The <literal>random</literal> and <literal>roundrobin</literal> filter
replace the
<link linkend="ini.mysqlnd-ms-plugin-config.pick"><literal>pick[]</literal></link>
directive used in prior version to select a load balancing policy.
The <literal>user</literal> filter replaces the
<function>mysqlnd_ms_set_user_pick_server</function> function.
</para>
<para>
Filters may accept parameters to refine their actions.
</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. No load balancing
policy is set and thus, defaulting takes place,
if neither the <literal>random</literal> nor the
<literal>roundrobin</literal> are part of a configuration section.
</para>
<para>
If a filter chain is configured so that a filter which output no
more than once server is used as input for a filter which should be given
more than one server as input, the plugin may emit a warning upon
opening a connection. The warning may read: <literal>(mysqlnd_ms) Error while creating
filter '%s' . Non-multi filter '%s' already created.
Stopping in %s on line %d</literal>. Futhermore an error of
the error code <literal>2000</literal>, the sql state <literal>HY000</literal>
and an error message similar to the warning may be set on the connection
handle.
</para>
<para>
<example>
<title>Invalid filter sequence</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
}
},
"filters": [
"roundrobin",
"random"
]
}
}
]]>
</programlisting>
<programlisting role="php">
<![CDATA[
<?php
$link = new mysqli("myapp", "root", "", "test");
printf("[%d] %s\n", mysqli_connect_errno(), mysqli_connect_error());
$link->query("SELECT 1 FROM DUAL");
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
PHP Warning: mysqli::mysqli(): (HY000/2000): (mysqlnd_ms) Error while creating filter 'random' . Non-multi filter 'roundrobin' already created. Stopping in filter_warning.php on line 1
[2000] (mysqlnd_ms) Error while creating filter 'random' . Non-multi filter 'roundrobin' already created. Stopping
PHP Warning: mysqli::query(): Couldn't fetch mysqli in filter_warning.php on line 3
]]>
</screen>
</example>
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.filter-random">
<term>
Filter: <parameter>random</parameter>
<type>object</type>
</term>
<listitem>
<para>
The <literal>random</literal> filter features the random and random once
load balancing policies, set through the
<link linkend="ini.mysqlnd-ms-plugin-config.pick"><literal>pick[]</literal></link>
directive in older versions.
</para>
<para>
The random policy will pick a random server whenever
a read-only statement is to be executed. The random once strategy
picks a random slave server once and continues using the slave for the
rest of the PHP web request. Random once is a default,
if load balancing is not configured through a filter.
</para>
<para>
If the <literal>random</literal> filter is not given any arguments, it
stands for random load balancing policy.
</para>
<para>
<example>
<title>Random load balancing with <literal>random</literal> filter</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
},
"slave_1": {
"host": "192.168.78.137",
"port": "3306"
}
},
"filters": [
"random"
]
}
}
]]>
</programlisting>
</example>
</para>
<para>
Optionally, the <literal>sticky</literal> argument can be passed to the
filter. If the parameter <literal>sticky</literal> is set to the string
<literal>1</literal>, the filter follows the random once
load balancing strategy.
</para>
<para>
<example>
<title>Random once load balancing with <literal>random</literal> filter</title>
<programlisting role="ini">
<![CDATA[
{
"filters": {
"random": {
"sticky": "1"
}
}
}
]]>
</programlisting>
</example>
</para>
<para>
Both the <literal>random</literal> and <literal>roundrobin</literal>
filters support setting a priority, a weight for a server, since
PECL/mysqlnd_ms 1.4.0. If the <literal>weight</literal> argument is
passed to the filter, it must assign a weight for all servers. Servers
must be given an alias name in the <literal>slave</literal> respectively
<literal>master</literal> server lists. The alias must be used
to reference servers for assigning a priority with <literal>weight</literal>.
</para>
<para>
<example>
<title>Referencing error</title>
<screen>
<![CDATA[
[E_RECOVERABLE_ERROR] mysqli_real_connect(): (mysqlnd_ms) Unknown server 'slave3' in 'random' filter configuration. Stopping in %s on line %d
]]>
</screen>
</example>
</para>
<para>
Using a wrong alias name with <literal>weight</literal> may result in
an error similar to the shown above.
</para>
<para>
If <literal>weight</literal> is omitted, the default weight of
all servers is one.
</para>
<para>
<example>
<title>Assigning a <literal>weight</literal> for load balancing</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master1":{
"host":"localhost",
"socket":"\/var\/run\/mysql\/mysql.sock"
}
},
"slave": {
"slave1": {
"host":"192.168.2.28",
"port":3306
},
"slave2": {
"host":"192.168.2.29",
"port":3306
},
"slave3": {
"host":"192.0.43.10",
"port":3306
},
},
"filters": {
"random": {
"weights": {
"slave1":8,
"slave2":4,
"slave3":1,
"master1":1
}
}
}
}
}
]]>
</programlisting>
</example>
</para>
<para>
At the average a server assigned a weight of two will be selected twice
as often as a server assigned a weight of one. Different weights can be
assigned to reflect differently sized machines, to prefer co-located slaves
which have a low network latency or, to configure a standby failover server.
In the latter case, you may want to assign the standby server a very low
weight in relation to the other servers. For example, given the
configuration above <literal>slave3</literal> will get only some eight
percent of the requests in the average. As long as <literal>slave1</literal>
and <literal>slave2</literal> are running, it will be used sparsely,
similar to a standby failover server. Upon failure of <literal>slave1</literal>
and <literal>slave2</literal>, the usage of <literal>slave3</literal>
increases. Please, check the notes on failover before using
<literal>weight</literal> this way.
</para>
<para>
Valid weight values range from 1 to 65535.
</para>
<para>
Unknown arguments are ignored by the filter. No warning or error is given.
</para>
<para>
The filter expects one or more servers as input. Outputs one server.
A filter sequence such as
<literal>random</literal>, <literal>roundrobin</literal> may
cause a warning and an error message to be set on the connection
handle when executing a statement.
</para>
<para>
List of filter arguments.
</para>
<informaltable>
<tgroup cols="3">
<colspec colwidth="1*"/>
<colspec colwidth="7*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Keyword</entry>
<entry>Description</entry>
<entry>Version</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>sticky</literal>
</entry>
<entry>
<para>
Enables or disabled random once load
balancing policy. See above.
</para>
</entry>
<entry>Since 1.2.0.</entry>
</row>
<row>
<entry>
<literal>weight</literal>
</entry>
<entry>
<para>
Assigns a load balancing weight/priority to
a server. Please, see above for a description.
</para>
</entry>
<entry>Since 1.4.0.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.filter-roundrobin">
<term>
Filter: <parameter>roundrobin</parameter>
<type>object</type>
</term>
<listitem>
<para>
If using the <literal>roundrobin</literal> filter, 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>
<example>
<title><literal>roundrobin</literal> filter</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
}
},
"filters": [
"roundrobin"
]
}
}
]]>
</programlisting>
</example>
</para>
<para>
Expects one or more servers as input. Outputs one server.
A filter sequence such as
<literal>roundrobin</literal>, <literal>random</literal> may
cause a warning and an error message to be set on the connection
handle when executing a statement.
</para>
<para>
List of filter arguments.
</para>
<informaltable>
<tgroup cols="3">
<colspec colwidth="1*"/>
<colspec colwidth="7*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Keyword</entry>
<entry>Description</entry>
<entry>Version</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>weight</literal>
</entry>
<entry>
<para>
Assigns a load balancing weight/priority to
a server. Please, find a description
<link linkend="ini.mysqlnd-ms-plugin-config-v2.filter-random">above</link>.
</para>
</entry>
<entry>Since 1.4.0.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.filter-user">
<term>
Filter: <parameter>user</parameter>
<type>object</type>
</term>
<listitem>
<para>
The <literal>user</literal> replaces
<function>mysqlnd_ms_set_user_pick_server</function> function,
which was removed in 1.1.0-beta. The filter sets a callback for user-defined
read/write splitting and server selection.
</para>
<para>
The plugins built-in read/write query split mechanism decisions can be
overwritten in two ways. The easiest way is to prepend a query string
with the SQL hints <constant>MYSQLND_MS_MASTER_SWITCH</constant>,
<constant>MYSQLND_MS_SLAVE_SWITCH</constant> or
<constant>MYSQLND_MS_LAST_USED_SWITCH</constant>. Using SQL hints one can
control, for example, whether a query shall be send to the MySQL replication
master server or one of the slave servers. By help of SQL hints it is
not possible to pick a certain slave server for query execution.
</para>
<para>
Full control on server selection can be gained using a callback function.
Use of a callback is recommended to expert users only because the callback
has to cover all cases otherwise handled by the plugin.
</para>
<para>
The plugin will invoke the callback function for selecting a server from the
lists of configured master and slave servers. The callback function
inspects the query to run and picks a server for query execution by returning
the hosts URI, as found in the master and slave list.
</para>
<para>
If the lazy connections are enabled and the callback chooses a slave server for
which no connection has been established so far and establishing the connection
to the slave fails, the plugin will return an error upon the next action
on the failed connection, for example, when running a query. It is the
responsibility of the application developer to handle the error. For example,
the application can re-run the query to trigger a new server selection and
callback invocation. If so, the callback must make sure to select
a different slave, or check slave availability, before returning to
the plugin to prevent an endless loop.
</para>
<para>
<example>
<title>Setting a callback</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
}
},
"filters": {
"user": {
"callback": "pick_server"
}
}
}
}
]]>
</programlisting>
</example>
</para>
<para>
The callback is supposed to return a host to run the query on.
The host URI is to be taken from the master and slave connection lists
passed to the callback function. If callback returns a value neither
found in the master nor in the slave connection lists the plugin
will emit an error of the type <literal>E_RECOVERABLE_ERROR</literal>
The error may read like
<literal> (mysqlnd_ms) User filter callback has returned an unknown server.
The server 'server that is not in master or slave list' can neither be found
in the master list nor in the slave list</literal>.
If the application catches the error to ignore it, follow up errors
may be set on the connection handle, for example,
<literal>(mysqlnd_ms) No connection selected by the last filter</literal> with
the error code <literal>2000</literal> and the sqlstate <literal>HY000</literal>.
Furthermore a warning may be emitted.
</para>
<para>
Referencing a non-existing function as a callback will result
in any error of the type <literal>E_RECOVERABLE_ERROR</literal> whenever
the plugin tries to callback function. The error message may reads like:
<literal>(mysqlnd_ms) Specified callback (pick_server) is
not a valid callback</literal>. If the application catches the error to
ignore it, follow up errors may be set on the connection handle, for example,
<literal>(mysqlnd_ms) Specified callback (pick_server) is
not a valid callback</literal> with the error code <literal>2000</literal>
and the sqlstate <literal>HY000</literal>. Furthermore a warning
may be emitted.
</para>
<para>
The following parameters are passed from the plugin to the callback.
</para>
<informaltable>
<tgroup cols="3">
<colspec colwidth="1*"/>
<colspec colwidth="7*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Parameter</entry>
<entry>Description</entry>
<entry>Version</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>connected_host</literal>
</entry>
<entry>
<para>
URI of the currently connected database server.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>query</literal>
</entry>
<entry>
<para>
Query string of the statement for which a server needs
to be picked.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>masters</literal>
</entry>
<entry>
<para>
List of master servers to choose from. Note, that the list of master
servers may not be identical to the list of configured master
servers if the filter is not the first in the filter chain.
Previously run filters may have reduced the master
list already.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>slaves</literal>
</entry>
<entry>
<para>
List of slave servers to choose from. Note, that the list of master
servers may not be identical to the list of configured master
servers if the filter is not the first in the filter chain.
Previously run filters may have reduced the master
list already.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>last_used_connection</literal>
</entry>
<entry>
<para>
URI of the server of the connection used to execute the previous
statement on.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>in_transaction</literal>
</entry>
<entry>
<para>
Boolean flag indicating whether the statement is
part of an open transaction. If autocommit mode is turned
off, this will be set to &true;. Otherwise
it is set to &false;.
</para>
<para>
Transaction detection is based on monitoring the
mysqlnd library call <literal>set_autocommit</literal>.
Monitoring is not possible before PHP 5.4.0. Please, see
<link linkend="mysqlnd-ms.pooling">connection pooling and switching</link>
concepts discussion for further details.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
<example>
<title>Using a callback</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.2.27",
"port": "3306"
},
"slave_1": {
"host": "192.168.78.136",
"port": "3306"
}
},
"filters": {
"user": {
"callback": "pick_server"
}
}
}
}
]]>
</programlisting>
<programlisting role="php">
<![CDATA[
<?php
function pick_server($connected, $query, $masters, $slaves, $last_used_connection, $in_transaction)
{
static $slave_idx = 0;
static $num_slaves = NULL;
if (is_null($num_slaves))
$num_slaves = count($slaves);
/* default: fallback to the plugins build-in logic */
$ret = NULL;
printf("User has connected to '%s'...\n", $connected);
printf("... deciding where to run '%s'\n", $query);
$where = mysqlnd_ms_query_is_select($query);
switch ($where)
{
case MYSQLND_MS_QUERY_USE_MASTER:
printf("... using master\n");
$ret = $masters[0];
break;
case MYSQLND_MS_QUERY_USE_SLAVE:
/* SELECT or SQL hint for using slave */
if (stristr($query, "FROM table_on_slave_a_only"))
{
/* a table which is only on the first configured slave */
printf("... access to table available only on slave A detected\n");
$ret = $slaves[0];
}
else
{
/* round robin */
printf("... some read-only query for a slave\n");
$ret = $slaves[$slave_idx++ % $num_slaves];
}
break;
case MYSQLND_MS_QUERY_LAST_USED:
printf("... using last used server\n");
$ret = $last_used_connection;
break;
}
printf("... ret = '%s'\n", $ret);
return $ret;
}
$mysqli = new mysqli("myapp", "root", "", "test");
if (!($res = $mysqli->query("SELECT 1 FROM DUAL")))
printf("[%d] %s\n", $mysqli->errno, $mysqli->error);
else
$res->close();
if (!($res = $mysqli->query("SELECT 2 FROM DUAL")))
printf("[%d] %s\n", $mysqli->errno, $mysqli->error);
else
$res->close();
if (!($res = $mysqli->query("SELECT * FROM table_on_slave_a_only")))
printf("[%d] %s\n", $mysqli->errno, $mysqli->error);
else
$res->close();
$mysqli->close();
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
User has connected to 'myapp'...
... deciding where to run 'SELECT 1 FROM DUAL'
... some read-only query for a slave
... ret = 'tcp://192.168.2.27:3306'
User has connected to 'myapp'...
... deciding where to run 'SELECT 2 FROM DUAL'
... some read-only query for a slave
... ret = 'tcp://192.168.78.136:3306'
User has connected to 'myapp'...
... deciding where to run 'SELECT * FROM table_on_slave_a_only'
... access to table available only on slave A detected
... ret = 'tcp://192.168.2.27:3306'
]]>
</screen>
</example>
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.filter-user-multi">
<term>
Filter: <parameter>user_multi</parameter>
<type>object</type>
</term>
<listitem>
<para>
The <literal>user_multi</literal> differs from the <literal>user</literal>
only in one aspect. Otherwise, their syntax is identical.
The <literal>user</literal> filter must pick
and return exactly one node for statement execution. A filter chain
usually ends with a filter that emits only one node. The filter chain
shall reduce the list of candidates for statement execution down to
one. This, only one node left, is the case after the <literal>user</literal>
filter has been run.
</para>
<para>
The <literal>user_multi</literal> filter is a multi filter. It returns a
list of slave and a list of master servers. This list needs further filtering
to identify exactly one node for statement execution. A multi filter is typically
placed at the top of the filter chain. The <literal>quality_of_service</literal>
filter is another example of a multi filter.
</para>
<para>
The return value of the callback set for <literal>user_multi</literal> must
be an an array with two elements. The first element holds a list of selected master
servers. The second element contains a list of selected slave servers. The
lists shall contain the keys of the slave and master servers as found in
the slave and master lists passed to the callback. The below example returns
random master and slave lists extracted from the functions input.
</para>
<para>
<example>
<title>Returning random masters and slaves</title>
<programlisting role="php">
<![CDATA[
<?php
function pick_server($connected, $query, $masters, $slaves, $last_used_connection, $in_transaction)
{
$picked_masters = array()
foreach ($masters as $key => $value) {
if (mt_rand(0, 2) > 1)
$picked_masters[] = $key;
}
$picked_slaves = array()
foreach ($slaves as $key => $value) {
if (mt_rand(0, 2) > 1)
$picked_slaves[] = $key;
}
return array($picked_masters, $picked_slaves);
}
?>
]]>
</programlisting>
</example>
</para>
<para>
The plugin will issue an
error of type <literal>E_RECOVERABLE</literal> if the callback fails to return
a server list. The error may read <literal>(mysqlnd_ms) User multi
filter callback has not returned a list of servers to use.
The callback must return an array in %s on line %d</literal>. In case the
server list is not empty but has invalid servers key/ids in it, an error
of type <literal>E_RECOVERABLE</literal> will the thrown with an
error message like <literal>(mysqlnd_ms) User multi filter callback
has returned an invalid list of servers to use.
Server id is negative in %s on line %d</literal>, or similar.
</para>
<para>
Whether an error is emitted in case of an empty slave or master list
depends on the configuration. If an empty master list is returned
for a write operation, it is likely that the plugin will emit a
warning that may read <literal>(mysqlnd_ms) Couldn't find the appropriate
master connection. 0 masters to choose from. Something is wrong in %s on line %d</literal>.
Typically a follow up error of type <literal>E_ERROR</literal> will happen.
In case of a read operation and an empty slave list the behavior depends
on the fail over configuration. If fail over to master is enabled, no
error should appear. If fail over to master is deactivated the plugin will
emit a warning that may read <literal>(mysqlnd_ms) Couldn't find the appropriate
slave connection. 0 slaves to choose from. Something is wrong in %s on line %d</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.filter-qos">
<term>
Filter: <parameter>quality_of_service</parameter>
<type>object</type>
</term>
<listitem>
<para>
The <literal>quality_of_service</literal> identifies cluster nodes
capable of delivering a certain quality of service. It is a multi filter
which returns zero, one or multiple of its input servers. Thus, it
must be followed by other filters to reduce the number of candidates
down to one for statement execution.
</para>
<para>
The <literal>quality_of_service</literal> filter has been introduced in 1.2.0-alpha.
In the 1.2 series the filters focus is on the consistency aspect of
service quality. Different types of clusters offer different
default data consistencies. For example, an asynchronous MySQL
replication slave offers eventual consistency. The slave may not
be able to deliver requested data because it has not replicated the write,
it may serve stale database because its lagging behind or it may serve
current information. Often, this is acceptable. In some cases
higher consistency levels are needed for the application to work correct.
In those cases, the <literal>quality_of_service</literal> can filter out cluster nodes
which cannot deliver the necessary quality of service.
</para>
<para>
The <literal>quality_of_service</literal> filter can be replaced or created
at runtime. A successful call to
<function>mysqlnd_ms_set_qos</function>
removes all existing <literal>qos</literal> filter entries from the
filter list and installs a new one at the very beginning. All settings
that can be made through
<function>mysqlnd_ms_set_qos</function>
can also be in the plugins configuration file. However, use of the function
is by far the most common use case. Instead of setting session consistency and
strong consistency service levels in the plugins configuration file it is
recommended to define only masters and no slaves. Both service levels will
force the use of masters only. Using an empty slave list shortens the
configuration file, thus improving readability. The only service level for which
there is a case of defining in the plugins configuration file is the combination
of eventual consistency and maximum slave lag.
</para>
<informaltable>
<tgroup cols="3">
<colspec colwidth="1*"/>
<colspec colwidth="7*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Keyword</entry>
<entry>Description</entry>
<entry>Version</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>eventual_consistency</literal>
</entry>
<entry>
<para>
Request eventual consistency. Allows the use of all
master and slave servers. Data returned may or may not be current.
</para>
<para>
Eventual consistency accepts an optional <literal>age</literal>
parameter. If <literal>age</literal> is given the plugin considers
only slaves for reading for which MySQL replication reports
a slave lag less or equal to <literal>age</literal>.
The replication lag is measure using <literal>SHOW SLAVE STATUS</literal>.
If the plugin fails to fetch the replication lag, the slave tested
is skipped. Implementation details and tips are given in the
<link linkend="mysqlnd-ms.qos-consistency">quality of service concepts section</link>.
</para>
<para>
Please note, if a filter chain
generates an empty slave list and the PHP configuration directive
<literal>mysqlnd_ms.multi_master=0</literal> is used, the plugin may
emit a warning.
</para>
<para>
<example>
<title>Global limit on slave lag</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.2.27",
"port": "3306"
},
"slave_1": {
"host": "192.168.78.136",
"port": "3306"
}
},
"filters": {
"quality_of_service": {
"eventual_consistency": {
"age":123
}
}
}
}
}
]]>
</programlisting>
</example>
</para>
</entry>
<entry>Since 1.2.0.</entry>
</row>
<row>
<entry>
<literal>session_consistency</literal>
</entry>
<entry>
<para>
Request session consistency (read your writes). Allows use of all masters
and all slaves which are in sync with the master.
If no further parameters are given slaves are filtered out
as there is no reliable way to test if a slave has caught up
to the master or is lagging behind. Please note, if a filter chain
generates an empty slave list and the PHP configuration directive
<literal>mysqlnd_ms.multi_master=0</literal> is used, the plugin may
emit a warning.
</para>
<para>
Session consistency temporarily requested using
<function>mysqlnd_ms_set_qos</function> is a valuable alternative
to using <literal>master_on_write</literal>.
<literal>master_on_write</literal> is likely to send more statements
to the master than needed. The application may be able to continue
operation at a lower consistency level after it has done
some critical reads.
</para>
</entry>
<entry>Since 1.1.0.</entry>
</row>
<row>
<entry>
<literal>strong_consistency</literal>
</entry>
<entry>
<para>
Request strong consistency. Only masters will be used.
</para>
</entry>
<entry>Since 1.2.0.</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.failover">
<term>
<parameter>failover</parameter>
Up to and including 1.3.x: <type>string</type>.
Since 1.4.0: <type>object</type>.
</term>
<listitem>
<para>
Failover policy. Supported policies:
<literal>disabled</literal> (default), <literal>master</literal>,
<literal>loop_before_master</literal> (Since 1.4.0).
</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>
Please note, the automatic failover logic is applied when opening
connections only. Once a connection has been opened no automatic attempts
are made to reopen it in case of an error. If, for example, the server
a connection is connected to is shut down and the user attempts to
run a statement on the connection, no automatic failover
will be tried. Instead, an error will be reported.
</para>
<para>
If using <literal>failover=master</literal> the plugin will implicitly
failover to a master, if available. Please check the
concepts documentation to learn about potential
pitfalls and risks of using <literal>failover=master</literal>.
</para>
<para>
<example>
<title>Optional master failover when failing to connect to slave (PECL/mysqlnd_ms &lt; 1.4.0)</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
}
},
"failover": "master"
}
}
]]>
</programlisting>
</example>
</para>
<para>
Since PECL/mysqlnd_ms 1.4.0 the failover configuration keyword refers to an
object.
</para>
<para>
<example>
<title>New syntax since 1.4.0</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
}
},
"failover": {"strategy": "master" }
}
}
]]>
</programlisting>
</example>
</para>
<informaltable>
<tgroup cols="3">
<colspec colwidth="1*"/>
<colspec colwidth="7*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Keyword</entry>
<entry>Description</entry>
<entry>Version</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>strategy</literal>
</entry>
<entry>
<para>
Failover policy. Possible values:
<literal>disabled</literal> (default), <literal>master</literal>,
<literal>loop_before_master</literal>
</para>
<para>
A value of <literal>disabled</literal> disables automatic failover.
</para>
<para>
Setting <literal>master</literal> instructs the plugin to try
to connect to a master in case of a slave connection error. If the
master connection attempt fails, the plugin exists the failover
loop and returns an error to the user.
</para>
<para>
If using <literal>loop_before_master</literal> and a slave request
is made, the plugin tries to connect to other slaves before failing
over to a master. If multiple master are given and multi master is enabled,
the plugin also loops over the list of masters and attempts to connect
before returning an error to the user.
</para>
</entry>
<entry>Since 1.4.0.</entry>
</row>
<row>
<entry>
<literal>remember_failed</literal>
</entry>
<entry>
<para>
Remember failures for the duration of a web request. Default:
<literal>false</literal>.
</para>
<para>
If set to <literal>true</literal> the plugin will remember failed
hosts and skip the hosts in all future load balancing made for
the duration of the current web request.
</para>
</entry>
<entry>
Since 1.4.0. Experimental feature. The feature is only available together
with the <literal>random</literal> and <literal>roundrobin</literal>
load balancing filter. The behavior and syntax is likely to change
in the future.
</entry>
</row>
<row>
<entry>
<literal>max_retries</literal>
</entry>
<entry>
<para>
Maximum number of connection attempts before skipping host.
Default: <literal>0</literal> (no limit).
</para>
<para>
The setting is used to prevent hosts from being dropped of the
host list upon the first failure. If set to <literal>n > 0</literal>,
the plugin will keep the node in the node list even after a failed
connection attempt. The node will not be removed immediately from the slave respectively
master lists after the first connection failure but instead be tried to
connect to up to <literal>n</literal> times in future load balancing rounds
before being removed.
</para>
</entry>
<entry>
Since 1.4.0. Experimental feature. The feature is only available together
with the <literal>random</literal> and <literal>roundrobin</literal>
load balancing filter. The behavior and syntax is likely to change
in the future.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
Setting <literal>failover</literal> to any other value but
<literal>disabled</literal>, <literal>master</literal> or
<literal>loop_before_master</literal>
will not emit any warning or error.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.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. Lazy connections are a default.
</para>
<para>
It is strongly recommended to use lazy connections.
Lazy connections help to keep 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.
Only some settings are &quot;remembered&quot; and applied when lazy
connections are opened.
</para>
<para>
<example>
<title>Disabling lazy connection</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
}
},
"lazy_connections": 0
}
}
]]>
</programlisting>
</example>
</para>
<para>
Please, see also <literal>server_charset</literal> to overcome potential
problems with string escaping and servers using different default
charsets.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.server-charset">
<term>
<parameter>server_charset</parameter>
<type>string</type>
</term>
<listitem>
<para>
The setting has been introduced in 1.4.0. It is recommended to set it
if using lazy connections.
</para>
<para>
The <literal>server_charset</literal> setting serves two purposes. It
acts as a fallback charset to be used for string escaping done before
a connection has been established and it helps to avoid escaping pitfalls
in heterogeneous environments which servers using different default charsets.
</para>
<para>
String escaping takes a connections charset into account. String escaping
is not possible before a connection has been opened and the connections
charset is known. The use of lazy connections delays the actual opening
of connections until a statement is send.
</para>
<para>
An application using lazy connections may attempt to escape a string
before sending a statement. In fact, this should be a common case as
the statement string may contain the string that is to be escaped.
However, due to the lazy connection feature no connection has been opened
yet and escaping fails. The plugin may report an error of the type
<literal>E_WARNING</literal> and a message like <literal>(mysqlnd_ms)
string escaping doesn't work without established connection.
Possible solution is to add server_charset to your configuration</literal>
to inform you of the pitfall.
</para>
<para>
Setting <literal>server_charset</literal> makes the plugin use
the given charset for string escaping done on lazy connection handles
before establishing a network connection to MySQL. Furthermore, the
plugin will enforce the use of the charset when the connection is
established.
</para>
<para>
Enforcing the use of the configured charset used for escaping is done
to prevent tapping into the pitfall of using a different charset for
escaping than used later for the connection. This has the additional
benefit of removing the need to align the charset configuration of all
servers used. No matter what the default charset on any of the servers is,
the plugin will set the configured one as a default.
</para>
<para>
The plugin does not stop the user from changing the charset at any time
using the <function>set_charset</function> call or corresponding SQL statements.
Please, note that the use of SQL is not recommended as it cannot be monitored
by the plugin. The user can, for example, change the charset on a
lazy connection handle after escaping a string and before the actual connection
is opened. The charset set by the user will be used for any subsequent escaping
before the connection is established. The connection will be established
using the configured charset, no matter what the server charset is or
what the user has set before. Once a connection has been opened,
<literal>set_charset</literal> is of no meaning anymore.
</para>
<para>
<example>
<title>String escaping on a lazy connection handle</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
}
},
"lazy_connections": 1,
"server_charset" : "utf8"
}
}
]]>
</programlisting>
<programlisting role="php">
<![CDATA[
<?php
$mysqli = new mysqli("myapp", "username", "password", "database");
$mysqli->real_escape("this will be escaped using the server_charset setting - utf8");
$mysqli->set_charset("latin1");
$mysqli->real_escape("this will be escaped using latin1");
/* server_charset implicitly set - utf8 connection */
$mysqli->query("SELECT 'This connection will be set to server_charset upon establishing' AS _msg FROM DUAL");
/* latin1 used from now on */
$mysqli->set_charset("latin1");
?>
]]>
</programlisting>
</example>
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.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>
<para>
<example>
<title>Master on write for consistent reads</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
}
},
"master_on_write": 1
}
}
]]>
</programlisting>
</example>
</para>
<para>
Please, note the <literal>quality_of_service</literal> filter introduced
in version 1.2.0-alpha. It gives finer control, for example, for achieving read-your-writes
and, it offers additional functionality introducing
<link linkend="mysqlnd-ms.qos-consistency">service levels</link>.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="ini.mysqlnd-ms-plugin-config-v2.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>
The setting requires 5.4.0 or newer. If used with PHP older than 5.4.0,
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 5.4.0 the mysqlnd library allows the plugin to monitor
the <literal>autocommit</literal> mode set by calls to the
libraries <literal>set_autocommit()</literal> function.
If setting <literal>set_stickiness=master</literal> and
<literal>autocommit</literal> gets disabled by a PHP MySQL extension
invoking the <literal>mysqlnd</literal> library internal
function call <literal>set_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>set_autocommit()</literal> is
<function>mysqli_autocommit</function>.
</para>
<para>
Although setting <literal>ser_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>
<para>
<example>
<title>Using master to execute transactions</title>
<programlisting role="ini">
<![CDATA[
{
"myapp": {
"master": {
"master_0": {
"host": "localhost"
}
},
"slave": {
"slave_0": {
"host": "192.168.78.136",
"port": "3306"
}
},
"trx_stickiness": "master"
}
}
]]>
</programlisting>
</example>
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</section>
<section xml:id="mysqlnd-ms.plugin-ini-v1">
<title xmlns="http://docbook.org/ns/docbook">Plugin configuration file (&lt;= 1.0.x)</title>
<note>
<para>
The below description applies to PECL/mysqlnd_ms &lt; 1.1.0-beta.
It is not valid for later versions.
</para>
</note>
<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 mimics standard the <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 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 remember 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 5.4.0 or newer. If used with PHP older than 5.4.0,
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 5.4.0 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>
<section xml:id="mysqlnd-ms.testing">
<title xmlns="http://docbook.org/ns/docbook">Testing</title>
<note>
<para>
The section applies to mysqlnd_ms 1.1.0 or newer, not the 1.0 series.
</para>
</note>
<para>
The PECL/mysqlnd_ms test suite is in the <filename>tests/</filename>
directory of the source distribution. The test suite consists of standard
phpt tests, which are described on the PHP Quality Assurance Teams website.
</para>
<para>
Running the tests requires setting up one to four MySQL servers. Some tests don't
connect to MySQL at all. Others require one server for testing. Some require
two distinct servers. In some cases two servers are used to emulate a
replication setup. In other cases a master and a slave of an existing MySQL replication
setup are required for testing. The tests will try to detect how many servers
and what kind of servers are given. If the required servers are not found, the
test will be skipped automatically.
</para>
<para>
Before running the tests, edit <filename>tests/config.inc</filename> to
configure the MySQL servers to be used for testing.
</para>
<para>
The most basic configuration is as follows.
<programlisting>
<![CDATA[
putenv("MYSQL_TEST_HOST=localhost");
putenv("MYSQL_TEST_PORT=3306");
putenv("MYSQL_TEST_USER=root");
putenv("MYSQL_TEST_PASSWD=");
putenv("MYSQL_TEST_DB=test");
putenv("MYSQL_TEST_ENGINE=MyISAM");
putenv("MYSQL_TEST_SOCKET=");
putenv("MYSQL_TEST_SKIP_CONNECT_FAILURE=1");
putenv("MYSQL_TEST_CONNECT_FLAGS=0");
putenv("MYSQL_TEST_EXPERIMENTAL=0");
/* replication cluster emulation */
putenv("MYSQL_TEST_EMULATED_MASTER_HOST=". getenv("MYSQL_TEST_HOST"));
putenv("MYSQL_TEST_EMULATED_SLAVE_HOST=". getenv("MYSQL_TEST_HOST"));
/* real replication cluster */
putenv("MYSQL_TEST_MASTER_HOST=". getenv("MYSQL_TEST_EMULATED_MASTER_HOST"));
putenv("MYSQL_TEST_SLAVE_HOST=". getenv("MYSQL_TEST_EMULATED_SLAVE_HOST"));
]]>
</programlisting>
</para>
<para>
<literal>MYSQL_TEST_HOST</literal>, <literal>MYSQL_TEST_PORT</literal> and
<literal>MYSQL_TEST_SOCKET</literal> define the hostname,
TCP/IP port and Unix domain socket of the default database server.
<literal>MYSQL_TEST_USER</literal> and <literal>MYSQL_TEST_PASSWD</literal>
contain the user and password needed to connect to the database/schema
configured with <literal>MYSQL_TEST_DB</literal>. All configured
servers must have the same database user configured to give access to
the test database.
</para>
<para>
Using <literal>host</literal>, <literal>host:port</literal> or <literal>host:/path/to/socket</literal>
syntax one can set an alternate host, host and port or host and socket for any
of the servers.
<programlisting>
<![CDATA[
putenv("MYSQL_TEST_SLAVE_HOST=192.168.78.136:3307"));
putenv("MYSQL_TEST_MASTER_HOST=myserver_hostname:/path/to/socket"));
]]>
</programlisting>
</para>
</section>
<section xml:id="mysqlnd-ms.debugging">
<title xmlns="http://docbook.org/ns/docbook">Debugging and Tracing</title>
<para>
The mysqlnd debug log can be used to debug and trace the actitivities of
PECL/mysqlnd_ms. As a mysqlnd PECL/mysqlnd_ms adds trace information to the
mysqlnd library debug file. Please, see the
<link linkend="mysqlnd.debug"><literal>mysqlnd.debug</literal></link>
PHP configuration directive documentation for a detailed description
on how to configure the debug log.
</para>
<para>
Configuration setting example to activate the debug log:
<programlisting>
<![CDATA[
mysqlnd.debug=d:t:x:O,/tmp/mysqlnd.trace
]]>
</programlisting>
<note>
<para>
This feature is only available with a debug build of PHP. Works
on Microsoft Windows if using a debug build of PHP and PHP was
built using Microsoft Visual C version 9 and above.
</para>
</note>
</para>
<para>
The debug log shows mysqlnd library and PECL/mysqlnd_ms plugin function calls,
similar to a trace log. Mysqlnd library calls are usually prefixed with
<literal>mysqlnd_</literal>. PECL/mysqlnd internal calls begin with
<literal>mysqlnd_ms</literal>.
</para>
<para>
Example excerpt from the debug log (connect):
<programlisting>
<![CDATA[
[...]
>mysqlnd_connect
| info : host=myapp user=root db=test port=3306 flags=131072
| >mysqlnd_ms::connect
| | >mysqlnd_ms_config_json_section_exists
| | | info : section=[myapp] len=[5]
| | | >mysqlnd_ms_config_json_sub_section_exists
| | | | info : section=[myapp] len=[5]
| | | | info : ret=1
| | | <mysqlnd_ms_config_json_sub_section_exists
| | | info : ret=1
| | <mysqlnd_ms_config_json_section_exists
[...]
]]>
</programlisting>
</para>
<para>
The debug log is not only useful for plugin developers but also to find the
cause of user errors. For example, if your application does not do proper
error handling and fails to record error messages, checking the debug
and trace log may help finding the cause. Use of the debug log
to debug application issues should be considered only if no other
option is available. Writing the debug log to disk is a slow
operation and may have negative impact on the application
performance.
</para>
<para>
Example excerpt from the debug log (connection failure):
<programlisting>
<![CDATA[
[...]
| | | | | | | info : adding error [Access denied for user 'root'@'localhost' (using password: YES)] to the list
| | | | | | | info : PACKET_FREE(0)
| | | | | | | info : PACKET_FREE(0x7f3ef6323f50)
| | | | | | | info : PACKET_FREE(0x7f3ef6324080)
| | | | | | <mysqlnd_auth_handshake
| | | | | | info : switch_to_auth_protocol=n/a
| | | | | | info : conn->error_info.error_no = 1045
| | | | | <mysqlnd_connect_run_authentication
| | | | | info : PACKET_FREE(0x7f3ef63236d8)
| | | | | >mysqlnd_conn::free_contents
| | | | | | >mysqlnd_net::free_contents
| | | | | | <mysqlnd_net::free_contents
| | | | | | info : Freeing memory of members
| | | | | | info : scheme=unix:///tmp/mysql.sock
| | | | | | >mysqlnd_error_list_pdtor
| | | | | | <mysqlnd_error_list_pdtor
| | | | | <mysqlnd_conn::free_contents
| | | | <mysqlnd_conn::connect
[...]
]]>
</programlisting>
</para>
<para>
The trace log can also be used to verify correct behaviour
of PECL/mysqlnd_ms itself, for example, to check which server has been
selected for query execution and why.
</para>
<para>
Example excerpt from the debug log (plugin decision):
<programlisting>
<![CDATA[
[...]
>mysqlnd_ms::query
| info : query=DROP TABLE IF EXISTS test
| >_mysqlnd_plugin_get_plugin_connection_data
| | info : plugin_id=5
| <_mysqlnd_plugin_get_plugin_connection_data
| >mysqlnd_ms_pick_server_ex
| | info : conn_data=0x7fb6a7d3e5a0 *conn_data=0x7fb6a7d410d0
| | >mysqlnd_ms_select_servers_all
| | <mysqlnd_ms_select_servers_all
| | >mysqlnd_ms_choose_connection_rr
| | | >mysqlnd_ms_query_is_select
[...]
| | | <mysqlnd_ms_query_is_select
[...]
| | | info : Init the master context
| | | info : list(0x7fb6a7d3f598) has 1
| | | info : Using master connection
| | | >mysqlnd_ms_advanced_connect
| | | | >mysqlnd_conn::connect
| | | | | info : host=localhost user=root db=test port=3306 flags=131072 persistent=0 state=0
]]>
</programlisting>
</para>
<para>
In this case the statement <literal>DROP TABLE IF EXISTS test</literal> has been
executed. Note that the statement string is shown in the log file. You may want
to take measures to restrict access to the log for security considerations.
</para>
<para>
The statement has been load balanced using round robin policy,
as you can easily guess from the functions name <literal>>mysqlnd_ms_choose_connection_rr</literal>.
It has been sent to a master server running on
<literal>host=localhost user=root db=test port=3306 flags=131072 persistent=0 state=0</literal>.
</para>
</section>
<section xml:id="mysqlnd-ms.monitoring">
<title xmlns="http://docbook.org/ns/docbook">Monitoring</title>
<para>
Plugin activity can be monitored using the mysqlnd trace log,
mysqlnd statistics, mysqlnd_ms plugin statistics and external PHP debugging tools.
Use of the trace log should be limited to debugging. It is recommended
to use the plugins statistics for monitoring.
</para>
<para>
Writing a trace log is a slow operation. If using an external PHP debugging tool,
please refer to the vendors manual about its performance impact and the
type of information collected. In many cases, external debugging tools will
provide call stacks. Often, a call stack or a trace log is more difficult to interpret
than the statistics provided by the plugin.
</para>
<para>
Plugin statistics tell how often which kind of cluster node has been used (slave or master),
why the node was used, if lazy connections have been used and if global transaction
ID injection has been performed. The monitoring information provided enables
user to verify plugin decisions and to plan their cluster resources based on usage pattern.
The function <function>mysqlnd_ms_get_stats</function>
is used to access the statistics. Please, see the functions description for a list
of available statistics.
</para>
<para>
Statistics are collected on a per PHP process basis. Their scope is a PHP process.
Depending on the PHP deployment model a process may serve one or multiple web requests.
If using CGI model, a PHP process serves one web request. If using FastCGI or
pre-fork web server models, a PHP process usually serves multiple web requests.
The same is the case with a threaded web server. Please, note that threads running
in parallel can update the statistics in parallel. Thus, if using a threaded PHP
deployment model, statistics can be changed by more than one script at a time. A
script cannot rely on the fact that it sees only its own changes to statistics.
</para>
<para>
<example>
<title>Verify plugin activity in a non-threaded deployment model</title>
<programlisting role="ini">
<![CDATA[
mysqlnd_ms.enable=1
mysqlnd_ms.collect_statistics=1
]]>
</programlisting>
<programlisting role="php">
<![CDATA[
<?php
/* Load balanced following "myapp" section rules from the plugins config file (not shown) */
$mysqli = new mysqli("myapp", "username", "password", "database");
if (mysqli_connect_errno())
/* Of course, your error handling is nicer... */
die(sprintf("[%d] %s\n", mysqli_connect_errno(), mysqli_connect_error()));
$stats_before = mysqlnd_ms_get_stats();
if ($res = $mysqli->query("SELECT 'Read request' FROM DUAL")) {
var_dump($res->fetch_all());
}
$stats_after = mysqlnd_ms_get_stats();
if ($stats_after['use_slave'] <= $stats_before['use_slave']) {
echo "According to the statistics the read request has not been run on a slave!";
}
?>
]]>
</programlisting>
</example>
</para>
<para>
Statistics are aggregated for all plugin activities and all connections handled by
the plugin. It is not possible to tell how much a certain connection handle has
contributed to the overall statistics.
</para>
<para>
Utilizing PHPs <function>register_shutdown_function</function> function or the
<literal>auto_append_file</literal> PHP configuration directive it is
easily possible to dump statistics into, for example, a log file when a script
finishes. Instead of using a log file it is also possible to send the statistics
to an external monitoring tool for recording and display.
</para>
<para>
<example>
<title>Recording statistics during shutdown</title>
<programlisting role="ini">
<![CDATA[
mysqlnd_ms.enable=1
mysqlnd_ms.collect_statistics=1
error_log=/tmp/php_errors.log
]]>
</programlisting>
<programlisting role="php">
<![CDATA[
<?php
function check_stats() {
$msg = str_repeat("-", 80) . "\n";
$msg .= var_export(mysqlnd_ms_get_stats(), true) . "\n";
$msg .= str_repeat("-", 80) . "\n";
error_log($msg);
}
register_shutdown_function("check_stats");
?>
]]>
</programlisting>
</example>
</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
-->
Reference in a new issue View git blame Copy permalink