Session Functions
PHP Manual

session_gc

Perform session data garbage collection

Description

int session_gc ( void )

session_gc is used to perform session data GC(garbage collection). PHP does probability based session GC by default.

Probability based GC works somewhat but it has few problems. 1) Low traffic site's session data may not be deleted within preferred duration. 2) High traffic site's may have too frequent GC. 3) GC is performed on the user's request and the user will experience GC delay.

Therefore, it is recommended to execute GC periodically for production systems. e.g. Use "cron" for UNIX like systems. Make sure to disable probability based GC by setting session.gc_probability to 0.

Return Values

session_gc returns number of deleted session data for success, FALSE for failure.

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.

Examples

Example #1 session_gc example for task managers like cron

<?php
// Note: This script should be executed by the same user of web server process.

// Need active session to initialize session data storage access.
session_start();

// Executes GC immediately
session_gc();

// Clean up session ID created by session_gc()
session_destroy();
?>

Example #2 session_gc example for user accessible script

<?php
// Note: session_gc() is recommended to be used by task manager script, but
// it may be used as follows.

// Used for last GC time check
$gc_time = '/tmp/php_session_last_gc';
$gc_period = 1800;

session_start();
// Execute GC only when GC period elapsed. 
// i.e. Calling session_gc() every request is waste of resources. 
if (file_exists($gc_time)) {
    if (filemtime($gc_time) < time() - $gc_period) {
        session_gc();
        touch($gc_time);
    }
} else {
    touch($gc_time);
}
?>

See Also