SESSION is stored in database usage instance, session storage instance_PHP tutorial

<&#63;php
/*
CREATE TABLE `ws_sessions` (
 `session_id` varchar(255) binary NOT NULL default '',
 `session_expires` int(10) unsigned NOT NULL default '0',
 `session_data` text,
 PRIMARY KEY (`session_id`)
) TYPE=InnoDB;
*/
class session {
 // session-lifetime
 var $lifeTime;
 // mysql-handle
 var $dbHandle;
 function open($savePath, $sessName) {
 // get session-lifetime
 $this->lifeTime = get_cfg_var("session.gc_maxlifetime");
 // open database-connection
 $dbHandle = @mysql_connect("localhost","root","");
 $dbSel = @mysql_select_db("test",$dbHandle);
 // return success
 if(!$dbHandle || !$dbSel)
  return false;
 $this->dbHandle = $dbHandle;
 return true;
 }
 function close() {
 $this->gc(ini_get('session.gc_maxlifetime'));
 // close database-connection
 return @mysql_close($this->dbHandle);
 }
 function read($sessID) {
 // fetch session-data
 $res = mysql_query("SELECT session_data AS d FROM ws_sessions
    WHERE session_id = '$sessID'
    AND session_expires > ".time(),$this->dbHandle);
 // return data or an empty string at failure
 if($row = mysql_fetch_assoc($res))
  return $row['d'];
 return "";
 }
 function write($sessID,$sessData) {
 // new session-expire-time
 $newExp = time() + $this->lifeTime;
 // is a session with this id in the database&#63;
 $res = mysql_query("SELECT * FROM ws_sessions
    WHERE session_id = '$sessID'",$this->dbHandle);
 // if yes,
 if(mysql_num_rows($res)) {
  // ...update session-data
  mysql_query("UPDATE ws_sessions
    SET session_expires = '$newExp',
    session_data = '$sessData'
    WHERE session_id = '$sessID'",$this->dbHandle);
  // if something happened, return true
  if(mysql_affected_rows($this->dbHandle))
  return true;
 }
 // if no session-data was found,
 else {
  // create a new row
  mysql_query("INSERT INTO ws_sessions (
    session_id,
    session_expires,
    session_data)
    VALUES(
    '$sessID',
    '$newExp',
    '$sessData')",$this->dbHandle);
  // if row was created, return true
  if(mysql_affected_rows($this->dbHandle))
  return true;
 }
 // an unknown error occured
 return false;
 }
 function destroy($sessID) {
 // delete session-data
 mysql_query("DELETE FROM ws_sessions WHERE session_id = '$sessID'",$this->dbHandle);
 // if session was deleted, return true,
 if(mysql_affected_rows($this->dbHandle))
  return true;
 // ...else return false
 return false;
 }
 function gc($sessMaxLifeTime) {
 // delete old sessions
 mysql_query("DELETE FROM ws_sessions WHERE session_expires < ".time(),$this->dbHandle);
 // return affected rows
 return mysql_affected_rows($this->dbHandle);
 }
}
$session = new session();
session_set_save_handler(array(&$session,"open"),
    array(&$session,"close"),
    array(&$session,"read"),
    array(&$session,"write"),
    array(&$session,"destroy"),
    array(&$session,"gc"));
session_start();
// etc...
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