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  <title>Transactions</title>

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</div><hr /><div id="mysqlnd-ms.quickstart.transactions" class="section">
  <h2 class="title">Transactions</h2>
  <p class="para">
   The current version of the plugin is not transaction safe by default,
   because it is not aware of running transactions in all cases. SQL transactions are
   units of work to be run on a single server. The plugin does not always know
   when the unit of work starts and when it ends. Therefore, the plugin may
   decide to switch connections in the middle of a transaction.
  </p>
  <p class="para">
   No kind of MySQL load balancer can detect transaction boundaries without any
   kind of hint from the application.
  </p>
  <p class="para">
   You can either use SQL hints to work around this limitation. Alternatively,
   you can activate transaction API call monitoring. In the latter case you
   must use API calls only to control transactions, see below.
  </p>
  <p class="para">
   <div class="example" id="example-1766">
    <p><strong>Example #1 Plugin config with one slave and one master</strong></p>
    <div class="example-contents">
<div class="inicode"><pre class="inicode">[myapp]
{
    &quot;myapp&quot;: {
        &quot;master&quot;: {
            &quot;master_0&quot;: {
                &quot;host&quot;: &quot;localhost&quot;,
                &quot;socket&quot;: &quot;\/tmp\/mysql.sock&quot;
            }
        },
        &quot;slave&quot;: {
            &quot;slave_0&quot;: {
                &quot;host&quot;: &quot;192.168.2.27&quot;,
                &quot;port&quot;: &quot;3306&quot;
            }
        }
    }
}</pre>
</div>
    </div>

   </div>
  </p>
  <p class="para">
   <div class="example" id="example-1767">
    <p><strong>Example #2 Using SQL hints for transactions</strong></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$mysqli&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">mysqli</span><span style="color: #007700">(</span><span style="color: #DD0000">"myapp"</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"username"</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"password"</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"database"</span><span style="color: #007700">);<br />if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">)<br />&nbsp;&nbsp;</span><span style="color: #FF8000">/*&nbsp;Of&nbsp;course,&nbsp;your&nbsp;error&nbsp;handling&nbsp;is&nbsp;nicer...&nbsp;*/<br />&nbsp;&nbsp;</span><span style="color: #007700">die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">mysqli_connect_errno</span><span style="color: #007700">(),&nbsp;</span><span style="color: #0000BB">mysqli_connect_error</span><span style="color: #007700">()));<br /><br /></span><span style="color: #FF8000">/*&nbsp;Not&nbsp;a&nbsp;SELECT,&nbsp;will&nbsp;use&nbsp;master&nbsp;*/<br /></span><span style="color: #007700">if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #DD0000">"START&nbsp;TRANSACTION"</span><span style="color: #007700">))&nbsp;{<br />&nbsp;</span><span style="color: #FF8000">/*&nbsp;Please&nbsp;use&nbsp;better&nbsp;error&nbsp;handling&nbsp;in&nbsp;your&nbsp;code&nbsp;*/<br />&nbsp;</span><span style="color: #007700">die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />}<br /><br /></span><span style="color: #FF8000">/*&nbsp;Prevent&nbsp;connection&nbsp;switch!&nbsp;*/<br /></span><span style="color: #007700">if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"/*%s*/INSERT&nbsp;INTO&nbsp;test(id)&nbsp;VALUES&nbsp;(1)"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">MYSQLND_MS_LAST_USED_SWITCH</span><span style="color: #007700">))))&nbsp;{<br />&nbsp;</span><span style="color: #FF8000">/*&nbsp;Please&nbsp;do&nbsp;proper&nbsp;ROLLBACK&nbsp;in&nbsp;your&nbsp;code,&nbsp;don't&nbsp;just&nbsp;die&nbsp;*/<br />&nbsp;</span><span style="color: #007700">die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />}<br />if&nbsp;(</span><span style="color: #0000BB">$res&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"/*%s*/SELECT&nbsp;COUNT(*)&nbsp;AS&nbsp;_num&nbsp;FROM&nbsp;test"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">MYSQLND_MS_LAST_USED_SWITCH</span><span style="color: #007700">))))&nbsp;{<br />&nbsp;&nbsp;</span><span style="color: #0000BB">$row&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$res</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">fetch_assoc</span><span style="color: #007700">();<br />&nbsp;&nbsp;</span><span style="color: #0000BB">$res</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">close</span><span style="color: #007700">();<br />&nbsp;&nbsp;if&nbsp;(</span><span style="color: #0000BB">$row</span><span style="color: #007700">[</span><span style="color: #DD0000">'_num'</span><span style="color: #007700">]&nbsp;&gt;&nbsp;</span><span style="color: #0000BB">1000</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"/*%s*/INSERT&nbsp;INTO&nbsp;events(task)&nbsp;VALUES&nbsp;('cleanup')"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">MYSQLND_MS_LAST_USED_SWITCH</span><span style="color: #007700">))))&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />&nbsp;&nbsp;&nbsp;}<br />&nbsp;&nbsp;}<br />}&nbsp;else&nbsp;{<br />&nbsp;die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />}<br />if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"/*%s*/UPDATE&nbsp;log&nbsp;SET&nbsp;last_update&nbsp;=&nbsp;NOW()"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">MYSQLND_MS_LAST_USED_SWITCH</span><span style="color: #007700">))))&nbsp;{<br />&nbsp;die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />}<br />if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"/*%s*/COMMIT"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">MYSQLND_MS_LAST_USED_SWITCH</span><span style="color: #007700">))))&nbsp;{<br />&nbsp;die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />}<br /><br /></span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">close</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
  </p>
  <p class="para">
   Starting with PHP 5.4.0, the <em>mysqlnd</em> library allows the
   plugin to monitor the status of the <em>autocommit</em> mode, if
   the mode is set by API calls instead of using SQL statements such as
   <em>SET AUTOCOMMIT=0</em>. This makes it possible for the plugin to
   become transaction aware. In this case, you do not need to use SQL hints.
  </p>
  <p class="para">
    If using PHP 5.4.0 or newer, API calls that enable <em>autocommit</em> mode,
    and when setting the plugin configuration option
    <a href="mysqlnd-ms.plugin-ini-json.html#ini.mysqlnd-ms-plugin-config-v2.trx-stickiness" class="link">trx_stickiness=master</a>,
    the plugin can automatically disable load balancing and connection switches
    for SQL transactions. In this configuration, the plugin stops load balancing
    if <em>autocommit</em> is disabled and directs all statements to
    the master. This prevents connection switches in the middle of
    a transaction. Once <em>autocommit</em> is re-enabled, the plugin
    starts to load balance statements again.
  </p>
   <p class="para">
   API based transaction boundary detection has been improved with PHP 5.5.0 and
   PECL/mysqlnd_ms 1.5.0 to cover not only calls to  <span class="function"><a href="mysqli.autocommit.html" class="function">mysqli_autocommit()</a></span>
   but also  <span class="function"><strong>mysqli_begin()</strong></span>,
    <span class="function"><a href="mysqli.commit.html" class="function">mysqli_commit()</a></span> and  <span class="function"><a href="mysqli.rollback.html" class="function">mysqli_rollback()</a></span>.
  </p>
  <p class="para">
   <div class="example" id="example-1768">
    <p><strong>Example #3 Transaction aware load balancing: trx_stickiness setting</strong></p>
    <div class="example-contents">
<div class="inicode"><pre class="inicode">{
    &quot;myapp&quot;: {
        &quot;master&quot;: {
            &quot;master_0&quot;: {
                &quot;host&quot;: &quot;localhost&quot;,
                &quot;socket&quot;: &quot;\/tmp\/mysql.sock&quot;
            }
        },
        &quot;slave&quot;: {
            &quot;slave_0&quot;: {
                &quot;host&quot;: &quot;127.0.0.1&quot;,
                &quot;port&quot;: &quot;3306&quot;
            }
        },
        &quot;trx_stickiness&quot;: &quot;master&quot;
    }
}</pre>
</div>
    </div>

   </div>
  </p>
  <p class="para">
   <div class="example" id="example-1769">
    <p><strong>Example #4 Transaction aware</strong></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$mysqli&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">mysqli</span><span style="color: #007700">(</span><span style="color: #DD0000">"myapp"</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"username"</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"password"</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"database"</span><span style="color: #007700">);<br />if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">)<br />&nbsp;&nbsp;</span><span style="color: #FF8000">/*&nbsp;Of&nbsp;course,&nbsp;your&nbsp;error&nbsp;handling&nbsp;is&nbsp;nicer...&nbsp;*/<br />&nbsp;&nbsp;</span><span style="color: #007700">die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">mysqli_connect_errno</span><span style="color: #007700">(),&nbsp;</span><span style="color: #0000BB">mysqli_connect_error</span><span style="color: #007700">()));<br /><br /></span><span style="color: #FF8000">/*&nbsp;Disable&nbsp;autocommit,&nbsp;plugin&nbsp;will&nbsp;run&nbsp;all&nbsp;statements&nbsp;on&nbsp;the&nbsp;master&nbsp;*/<br /></span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">autocommit</span><span style="color: #007700">(</span><span style="color: #0000BB">FALSE</span><span style="color: #007700">);<br /><br />if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #DD0000">"INSERT&nbsp;INTO&nbsp;test(id)&nbsp;VALUES&nbsp;(1)"</span><span style="color: #007700">))&nbsp;{<br />&nbsp;</span><span style="color: #FF8000">/*&nbsp;Please&nbsp;do&nbsp;proper&nbsp;ROLLBACK&nbsp;in&nbsp;your&nbsp;code,&nbsp;don't&nbsp;just&nbsp;die&nbsp;*/<br />&nbsp;</span><span style="color: #007700">die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />}<br />if&nbsp;(</span><span style="color: #0000BB">$res&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #DD0000">"SELECT&nbsp;COUNT(*)&nbsp;AS&nbsp;_num&nbsp;FROM&nbsp;test"</span><span style="color: #007700">))&nbsp;{<br />&nbsp;&nbsp;</span><span style="color: #0000BB">$row&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$res</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">fetch_assoc</span><span style="color: #007700">();<br />&nbsp;&nbsp;</span><span style="color: #0000BB">$res</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">close</span><span style="color: #007700">();<br />&nbsp;&nbsp;if&nbsp;(</span><span style="color: #0000BB">$row</span><span style="color: #007700">[</span><span style="color: #DD0000">'_num'</span><span style="color: #007700">]&nbsp;&gt;&nbsp;</span><span style="color: #0000BB">1000</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #DD0000">"INSERT&nbsp;INTO&nbsp;events(task)&nbsp;VALUES&nbsp;('cleanup')"</span><span style="color: #007700">))&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />&nbsp;&nbsp;&nbsp;}<br />&nbsp;&nbsp;}<br />}&nbsp;else&nbsp;{<br />&nbsp;die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />}<br />if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #DD0000">"UPDATE&nbsp;log&nbsp;SET&nbsp;last_update&nbsp;=&nbsp;NOW()"</span><span style="color: #007700">))&nbsp;{<br />&nbsp;die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />}<br />if&nbsp;(!</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">commit</span><span style="color: #007700">())&nbsp;{<br />&nbsp;die(</span><span style="color: #0000BB">sprintf</span><span style="color: #007700">(</span><span style="color: #DD0000">"[%d]&nbsp;%s\n"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">errno</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">error</span><span style="color: #007700">));<br />}<br /><br /></span><span style="color: #FF8000">/*&nbsp;Plugin&nbsp;assumes&nbsp;that&nbsp;the&nbsp;transaction&nbsp;has&nbsp;ended&nbsp;and&nbsp;starts&nbsp;load&nbsp;balancing&nbsp;again&nbsp;*/<br /></span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">autocommit</span><span style="color: #007700">(</span><span style="color: #0000BB">TRUE</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">close</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
  </p>
  <blockquote class="note"><p><strong class="note">Note</strong>: 
   <strong>Version requirement</strong><br />
   <p class="para">
    The plugin configuration option
    <a href="mysqlnd-ms.plugin-ini-json.html#ini.mysqlnd-ms-plugin-config-v2.trx-stickiness" class="link">trx_stickiness=master</a>
    requires PHP 5.4.0 or newer.
   </p>
  </p></blockquote>
  <p class="para">
   Please note the restrictions outlined in the
   <a href="mysqlnd-ms.transaction.html" class="link">transaction handling</a> concepts
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