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Nov 10, 2025
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Improve session_gc documentation #4970

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1d831a7
Improve session_gc documentation
jbafford Nov 1, 2025
bba242d
Style updates
jbafford Nov 1, 2025
ff23c57
Remove redundant simpara wrappers, fix whitespace
jbafford Nov 4, 2025
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105 changes: 56 additions & 49 deletions reference/session/functions/session-gc.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -11,25 +11,34 @@
<type class="union"><type>int</type><type>false</type></type><methodname>session_gc</methodname>
<void/>
</methodsynopsis>
<para>
<function>session_gc</function> is used to perform session data
GC (garbage collection). PHP does probability based session GC by
default.
</para>
<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.
</para>
<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
<link linkend="ini.session.gc-probability">session.gc_probability</link>
to 0.
</para>
<simpara>
By default, PHP uses <link linkend="ini.session.gc-probability">session.gc_probability</link>
to run the session garbage collector probabilistically on each
request. There are some limitations with this approach:
</simpara>
<simplelist>
<member>Low traffic sites may not have their session data deleted within the preferred duration.</member>
<member>High traffic sites may have the garbage collector run too frequently, performing unnecessary extra work.</member>
<member>Garbage collection is performed on the user's request, and the user may experience a delay.</member>
</simplelist>
<simpara>
For production systems, it is recommended to disable the
probability-based garbage collection by setting
<link linkend="ini.session.gc-probability">session.gc_probability</link> to <literal>0</literal>
and explicitly trigger the garbage collector periodically, for example by using "cron" on
UNIX-like systems to run a script that calls <function>session_gc</function>.
</simpara>

<note>
<simpara>
When calling <function>session_gc</function> from a command-line php script,
the <link linkend="ini.session.save-path">session.save_path</link> must be set
to the same value as web requests, and the script must have access and delete
permissions for the session files. This may be affected by the user the script runs as,
and container or sandboxing features such as systemd's <literal>PrivateTmp=</literal>
option.
</simpara>
</note>
</refsect1>

<refsect1 role="parameters">
Expand All @@ -39,23 +48,24 @@

<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
<function>session_gc</function> returns number of deleted session
data for success, &false; for failure.
</para>
<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.
</para>
<simpara>
<function>session_gc</function> returns the number of deleted session
entries on success, &return.falseforfailure;.
</simpara>
<note>
<simpara>
Old session save handlers do not return the number of deleted session entries, but
rather only a success/failure flag. If this is the case, <literal>1</literal> is returned regardless of
how many session entries are actually deleted.
</simpara>
</note>
</refsect1>

<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title><function>session_gc</function> example for task managers like cron</title>
<programlisting role="php">
<example>
<title><function>session_gc</function> example for task managers like cron</title>
<programlisting role="php">
<![CDATA[
<?php
// Note: This script should be executed by the same user of web server process.
Expand All @@ -66,18 +76,18 @@ session_start();
// Executes GC immediately
session_gc();

// Clean up session ID created by session_gc()
// Clean up session ID created by session_start()
session_destroy();
?>
]]>
</programlisting>
</example>
<example>
<title><function>session_gc</function> example for user accessible script</title>
<programlisting role="php">
</programlisting>
</example>
<example>
<title><function>session_gc</function> example for user accessible script</title>
<programlisting role="php">
<![CDATA[
<?php
// Note: session_gc() is recommended to be used by task manager script, but
// Note: session_gc() is recommended to be used by a task manager script, but
// it may be used as follows.

// Used for last GC time check
Expand All @@ -97,20 +107,17 @@ if (file_exists($gc_time)) {
}
?>
]]>
</programlisting>
</example>
</para>
</programlisting>
</example>
</refsect1>

<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>session_start</function></member>
<member><function>session_destroy</function></member>
<member><link linkend="ini.session.gc-probability">session.gc_probability</link></member>
</simplelist>
</para>
<simplelist>
<member><function>session_start</function></member>
<member><function>session_destroy</function></member>
<member><link linkend="ini.session.gc-probability">session.gc_probability</link></member>
</simplelist>
</refsect1>
</refentry>
<!-- Keep this comment at the end of the file
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