Let's have a look at an actual custom session backend. This uses MySQL to store the session data. We could set these right in the script, but let's make use of Apache's httpd.conf file to set our custom save handler for a portion of our web site. 

<Directory "/var/html/test">
    php_value session.save_handler user
    php_value session.save_path mydb
    php_value session.name sessions
</Directory>
The MySQL schema looks like this:
CREATE TABLE sessions (
	id char(32) NOT NULL,
	data text,
	ts timestamp,
	PRIMARY KEY (id)
)
We can now write our handler. It looks like this:
<?php
function open($db,$name) {
    global $table;
    mysql_connect('localhost');
    mysql_select_db($db);
    $table = $name;
    return true;
}

function close() {
    mysql_close();
    return true;
}

function read($id) {
    global $table;
    $result = mysql_query("select data from $table where id='$id'");
    if($result && mysql_num_rows($result)) {
        return mysql_result($result,0);
    } else {
        error_log("read: ".mysql_error()."\n",3,"/tmp/errors.log");
        return "";
    }
}

function write($id, $data) {
    global $table;
    $data = addslashes($data);
    mysql_query("replace into $table (id,data) values('$id','$data')") 
      or error_log("write: ".mysql_error()."\n",3,"/tmp/errors.log");
    return true;
}

function destroy($id) {
    global $table;
    mysql_query("delete from $table where where id='$id'"); 
}

function gc($max_time) {
    global $table;
    mysql_query(
      "delete from $table where 
       UNIX_TIMESTAMP(ts)<UNIX_TIMESTAMP()-$max_time") 
      or error_log("gc: ".mysql_error(). "\n",3,"/tmp/errors.log");
    return true;
}

session_set_save_handler('open','close','read','write','destroy','gc');
?>
Our PHP files under /var/html/test then simply need to look something like this: 

<?php
  require 'handler.php';

  session_start();
  session_register('var');
  $var = "Hello World";
?>