session_gc
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 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.
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 session.gc_probability to 0.
Parameters
This function has no parameters.
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.