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<title>Perform session data garbage collection</title>
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<h1 class="refname">session_gc</h1>
<p class="verinfo">(PHP 7 >= 7.1.0)</p><p class="refpurpose"><span class="refname">session_gc</span> — <span class="dc-title">Perform session data garbage collection</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.session-gc-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">int</span> <span class="methodname"><strong>session_gc</strong></span>
( <span class="methodparam">void</span>
)</div>
<p class="para rdfs-comment">
<span class="function"><strong>session_gc()</strong></span> is used to perform session data
GC(garbage collection). PHP does probability based session GC by
default.
</p>
<p class="para">
Probability based GC works somewhat but it has few problems. 1) Low
traffic sites' session data may not be deleted within the preferred
duration. 2) High traffic sites' GC may be too frequent GC. 3) GC is
performed on the user's request and the user will experience a GC
delay.
</p>
<p class="para">
Therefore, it is recommended to execute GC periodically for
production systems using, e.g., "cron" for UNIX-like systems.
Make sure to disable probability based GC by setting
<a href="session.configuration.html#ini.session.gc-probability" class="link">session.gc_probability</a>
to 0.
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.session-gc-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
<span class="function"><strong>session_gc()</strong></span> returns number of deleted session
data for success, <strong><code>FALSE</code></strong> for failure.
</p>
<p class="para">
Old save handlers do not return number of deleted session data, but
only success/failure flag. If this is the case, number of deleted
session data became 1 regardless of actually deleted data.
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.session-gc-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-5960">
<p><strong>Example #1 <span class="function"><strong>session_gc()</strong></span> example for task managers like cron</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">// Note: This script should be executed by the same user of web server process.<br /><br />// Need active session to initialize session data storage access.<br /></span><span style="color: #0000BB">session_start</span><span style="color: #007700">();<br /><br /></span><span style="color: #FF8000">// Executes GC immediately<br /></span><span style="color: #0000BB">session_gc</span><span style="color: #007700">();<br /><br /></span><span style="color: #FF8000">// Clean up session ID created by session_gc()<br /></span><span style="color: #0000BB">session_destroy</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<div class="example" id="example-5961">
<p><strong>Example #2 <span class="function"><strong>session_gc()</strong></span> example for user accessible script</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">// Note: session_gc() is recommended to be used by task manager script, but<br />// it may be used as follows.<br /><br />// Used for last GC time check<br /></span><span style="color: #0000BB">$gc_time </span><span style="color: #007700">= </span><span style="color: #DD0000">'/tmp/php_session_last_gc'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$gc_period </span><span style="color: #007700">= </span><span style="color: #0000BB">1800</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">session_start</span><span style="color: #007700">();<br /></span><span style="color: #FF8000">// Execute GC only when GC period elapsed. <br />// i.e. Calling session_gc() every request is waste of resources. <br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">file_exists</span><span style="color: #007700">(</span><span style="color: #0000BB">$gc_time</span><span style="color: #007700">)) {<br /> if (</span><span style="color: #0000BB">filemtime</span><span style="color: #007700">(</span><span style="color: #0000BB">$gc_time</span><span style="color: #007700">) < </span><span style="color: #0000BB">time</span><span style="color: #007700">() - </span><span style="color: #0000BB">$gc_period</span><span style="color: #007700">) {<br /> </span><span style="color: #0000BB">session_gc</span><span style="color: #007700">();<br /> </span><span style="color: #0000BB">touch</span><span style="color: #007700">(</span><span style="color: #0000BB">$gc_time</span><span style="color: #007700">);<br /> }<br />} else {<br /> </span><span style="color: #0000BB">touch</span><span style="color: #007700">(</span><span style="color: #0000BB">$gc_time</span><span style="color: #007700">);<br />}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.session-gc-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"><span class="function"><a href="function.session-start.html" class="function" rel="rdfs-seeAlso">session_start()</a> - Start new or resume existing session</span></li>
<li class="member"><span class="function"><a href="function.session-destroy.html" class="function" rel="rdfs-seeAlso">session_destroy()</a> - Destroys all data registered to a session</span></li>
<li class="member"><a href="session.configuration.html#ini.session.gc-probability" class="link">session.gc_probability</a></li>
</ul>
</p>
</div>
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