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<h1 class="refname">mysqlnd_ms_set_qos</h1>
<p class="verinfo">(PECL mysqlnd_ms < 1.2.0)</p><p class="refpurpose"><span class="refname">mysqlnd_ms_set_qos</span> — <span class="dc-title">Sets the quality of service needed from the cluster</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.mysqlnd-ms-set-qos-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">bool</span>
<span class="methodname"><strong>mysqlnd_ms_set_qos</strong></span>
( <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$connection</code></span>
, <span class="methodparam"><span class="type">int</span> <code class="parameter">$service_level</code></span>
[, <span class="methodparam"><span class="type">int</span> <code class="parameter">$service_level_option</code></span>
[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$option_value</code></span>
]] )</div>
<p class="para rdfs-comment">
Sets the quality of service needed from the cluster. A database cluster delivers
a certain quality of service to the user depending on its architecture. A major
aspect of the quality of service is the consistency level the cluster can offer.
An asynchronous MySQL replication cluster defaults to eventual consistency for
slave reads: a slave may serve stale data, current data, or it may have not the
requested data at all, because it is not synchronous to the master. In a
MySQL replication cluster, only master accesses can give strong consistency, which
promises that all clients see each others changes.
</p>
<p class="para">
PECL/mysqlnd_ms hides the complexity of choosing appropriate nodes to achieve
a certain level of service from the cluster. The
"Quality of Service" filter implements the necessary logic. The filter can either
be configured in the plugins configuration file, or at runtime using
<span class="function"><strong>mysqlnd_ms_set_qos()</strong></span>.
</p>
<p class="para">
Similar results can be achieved with PECL mysqlnd_ms < 1.2.0, if using
SQL hints to force the use of a certain type of node or using the
<em>master_on_write</em> plugin configuration option. The first
requires more code and causes more work on the application side.
The latter is less refined than using the quality of service filter.
Settings made through the function call can be reversed, as shown in the example
below. The example temporarily switches to a higher service level
(session consistency, read your writes) and returns
back to the clusters default after it has performed all operations that require the
better service. This way, read load on the master can be minimized compared to
using <em>master_on_write</em>, which would continue using the master
after the first write.
</p>
<p class="para">
Since 1.5.0 calls will fail when done in the middle of a transaction if
<a href="mysqlnd-ms.plugin-ini-json.html#ini.mysqlnd-ms-plugin-config-v2.trx-stickiness" class="link">transaction stickiness</a>
is enabled and transaction boundaries have been detected.
properly.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.mysqlnd-ms-set-qos-parameters">
<h3 class="title">Parameters</h3>
<dl>
<dt>
<span class="term"><em><code class="parameter">connection</code></em></span>
<dd>
<p class="para">
A PECL/mysqlnd_ms connection handle to a MySQL server of the type
<a href="ref.pdo-mysql.html" class="link">PDO_MYSQL</a>, <a href="book.mysqli.html" class="link">mysqli</a> or
<a href="book.mysql.html" class="link">ext/mysql</a> for which a service level is to be set.
The connection handle is obtained when opening a connection with
a host name that matches a mysqlnd_ms configuration file
entry using any of the above three MySQL driver extensions.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">service_level</code></em></span>
<dd>
<p class="para">
The requested service level: <strong><code>MYSQLND_MS_QOS_CONSISTENCY_EVENTUAL</code></strong>,
<strong><code>MYSQLND_MS_QOS_CONSISTENCY_SESSION</code></strong> or
<strong><code>MYSQLND_MS_QOS_CONSISTENCY_STRONG</code></strong>.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">service_level_option</code></em></span>
<dd>
<p class="para">
An option to parameterize the requested service level.
The option can either be <strong><code>MYSQLND_MS_QOS_OPTION_GTID</code></strong>
or <strong><code>MYSQLND_MS_QOS_OPTION_AGE</code></strong>.
</p>
<p class="para">
The option <strong><code>MYSQLND_MS_QOS_OPTION_GTID</code></strong> can be used
to refine the service level <strong><code>MYSQLND_MS_QOS_CONSISTENCY_SESSION</code></strong>.
It must be combined with a fourth function parameter, the
<em><code class="parameter">option_value</code></em>. The <em><code class="parameter">option_value</code></em>
shall be a global transaction ID obtained from
<span class="function"><a href="function.mysqlnd-ms-get-last-gtid.html" class="function">mysqlnd_ms_get_last_gtid()</a></span>. If set, the
plugin considers both master servers and asynchronous slaves for session
consistency (read your writes). Otherwise, only masters are
used to achieve session consistency. A slave is considered up-to-date and
checked if it has already replicated the global transaction ID from
<em><code class="parameter">option_value</code></em>. Please note, searching appropriate slaves
is an expensive and slow operation. Use the feature sparsely, if the
master cannot handle the read load alone.
</p>
<p class="para">
The <strong><code>MYSQLND_MS_QOS_OPTION_AGE</code></strong> option can be combined
with the <strong><code>MYSQLND_MS_QOS_CONSISTENCY_EVENTUAL</code></strong>
service level, to filter out asynchronous slaves that lag more seconds behind
the master than <em><code class="parameter">option_value</code></em>. If set, the plugin
will only consider slaves for reading if
<em>SHOW SLAVE STATUS</em> reports
<em>Slave_IO_Running=Yes</em>,
<em>Slave_SQL_Running=Yes</em> and
<em>Seconds_Behind_Master <= option_value</em>. Please note,
searching appropriate slaves is an expensive and slow operation.
Use the feature sparsely in version 1.2.0. Future versions may improve the
algorithm used to identify candidates. Please, see the MySQL reference
manual about the precision, accuracy and limitations of the MySQL administrative
command <em>SHOW SLAVE STATUS</em>.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">option_value</code></em></span>
<dd>
<p class="para">
Parameter value for the service level option. See also the
<em><code class="parameter">service_level_option</code></em> parameter.
</p>
</dd>
</dt>
</dl>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.mysqlnd-ms-set-qos-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns <strong><code>TRUE</code></strong> if the connections service level
has been switched to the requested. Otherwise, returns <strong><code>FALSE</code></strong>
</p>
</div>
<div class="refsect1 unknown-returnvaluet" id="refsect1-function.mysqlnd-ms-set-qos-unknown-returnvaluet">
<h3 class="title">Notes</h3>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
<span class="function"><strong>mysqlnd_ms_set_qos()</strong></span> requires
PHP >= 5.4.0 and PECL mysqlnd_ms >= 1.2.0. Internally, it is using
a <em>mysqlnd</em> library C functionality not available with PHP 5.3.
</p>
</p></blockquote>
</div>
<div class="refsect1 examples" id="refsect1-function.mysqlnd-ms-set-qos-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-1843">
<p><strong>Example #1 <span class="function"><strong>mysqlnd_ms_set_qos()</strong></span> example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">/* Open mysqlnd_ms connection using mysqli, PDO_MySQL or mysql extension */<br /></span><span style="color: #0000BB">$mysqli </span><span style="color: #007700">= new </span><span style="color: #0000BB">mysqli</span><span style="color: #007700">(</span><span style="color: #DD0000">"myapp"</span><span style="color: #007700">, </span><span style="color: #DD0000">"username"</span><span style="color: #007700">, </span><span style="color: #DD0000">"password"</span><span style="color: #007700">, </span><span style="color: #DD0000">"database"</span><span style="color: #007700">);<br />if (!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">)<br /> </span><span style="color: #FF8000">/* Of course, your error handling is nicer... */<br /> </span><span style="color: #007700">die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d] %s\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">mysqli_connect_errno</span><span style="color: #007700">(), </span><span style="color: #0000BB">mysqli_connect_error</span><span style="color: #007700">()));<br /><br /></span><span style="color: #FF8000">/* Session consistency: read your writes */<br /></span><span style="color: #0000BB">$ret </span><span style="color: #007700">= </span><span style="color: #0000BB">mysqlnd_ms_set_qos</span><span style="color: #007700">(</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">, </span><span style="color: #0000BB">MYSQLND_MS_QOS_CONSISTENCY_SESSION</span><span style="color: #007700">);<br />if (!</span><span style="color: #0000BB">$ret</span><span style="color: #007700">)<br /> die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d] %s\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">errno</span><span style="color: #007700">, </span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">error</span><span style="color: #007700">));<br /><br /></span><span style="color: #FF8000">/* Will use master and return fresh data, client can see his last write */<br /></span><span style="color: #007700">if (!</span><span style="color: #0000BB">$res </span><span style="color: #007700">= </span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #DD0000">"SELECT item, price FROM orders WHERE order_id = 1"</span><span style="color: #007700">))<br /> die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d] %s\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">errno</span><span style="color: #007700">, </span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">error</span><span style="color: #007700">));<br /><br /></span><span style="color: #FF8000">/* Back to default: use of all slaves and masters permitted, stale data can happen */<br /></span><span style="color: #007700">if (!</span><span style="color: #0000BB">mysqlnd_ms_set_qos</span><span style="color: #007700">(</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">, </span><span style="color: #0000BB">MYSQLND_MS_QOS_CONSISTENCY_EVENTUAL</span><span style="color: #007700">))<br /> die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d] %s\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">errno</span><span style="color: #007700">, </span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">error</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.mysqlnd-ms-set-qos-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member">
<span class="function"><a href="function.mysqlnd-ms-get-last-gtid.html" class="function" rel="rdfs-seeAlso">mysqlnd_ms_get_last_gtid()</a> - Returns the latest global transaction ID</span>
</li>
<li class="member">
<a href="mysqlnd-ms.qos-consistency.html" class="link">Service level and consistency concept</a>
</li>
<li class="member">
<a href="mysqlnd-ms.filter.html" class="link">Filter concept</a>
</li>
</ul>
</p>
</div>
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