


How Does PHP\'s Session Garbage Collector Affect Session Lifespan?
Nov 08, 2024 am 08:52 AMSession Lifespan Determination
Question:
How can you determine the duration of a session based on the following PHP configuration settings?
session.auto_start Off Off session.bug_compat_42 Off Off session.bug_compat_warn On On session.cache_expire 180 180 session.cache_limiter nocache nocache session.cookie_domain no value no value session.cookie_httponly Off Off session.cookie_lifetime 0 0 session.cookie_path / / session.cookie_secure Off Off session.entropy_file no value no value session.entropy_length 0 0 session.gc_divisor 1000 1000 session.gc_maxlifetime 1440 1440 session.gc_probability 1 1 session.hash_bits_per_character 5 5 session.hash_function 0 0 session.name PHPSESSID PHPSESSID session.referer_check no value no value session.save_handler files files session.save_path /var/lib/php/session /var/lib/php/session session.serialize_handler php php session.use_cookies On On session.use_only_cookies Off Off session.use_trans_sid 0 0
Answer:
While the session.gc_maxlifetime setting specifies the maximum lifetime of session data since its last change, PHP's session handling has some complexities.
Specifically, the garbage collector that removes expired session data is not called by every session_start call. Instead, it is invoked with a probability determined by session.gc_probability (default: 1) and session.gc_divisor (default: 100). This means that even if session data has expired theoretically, it may still be used for a longer period.
To mitigate this issue and ensure reliable session timeouts, it is recommended to implement a custom session timeout mechanism.
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