session_set_save_handler() sets the user-level session storage functions which are used for storing and retrieving data associated with a session. This is most useful when a storage method other than those supplied by PHP sessions is preferred. i.e. Storing the session data in a local database. Returns TRUE on success or FALSE on failure.
Note: The "write" handler is not executed until after the output stream is closed. Thus, output from debugging statements in the "write" handler will never be seen in the browser. If debugging output is necessary, it is suggested that the debug output be written to a file instead.
The following example provides file based session
storage similar to the PHP sessions default save handler
files. This example could easily be
extended to cover database storage using your favorite PHP
supported database engine.
Read function must return string value always to make save handler work as expected. Return empty string if there is no data to read. Return values from other handlers are converted to boolean expression. TRUE for success, FALSE for failure.
Write and Close handlers are called after destructing objects since PHP 5.0.5. Thus destructors can use sessions but session handler can't use objects. In prior versions, they were called in the opposite order. It is possible to call session_write_close() from the destructor to solve this chicken and egg problem.
Example 1. session_set_save_handler() example
See also the session.save_handler configuration directive.