MySQL Pool Maste/Slave

MySQL.pool.php

class DB {
       private static $cfg = array(
           'write' =>
               array('mysql:dbname=MyDB;host=10.1.2.3'),
           'read' =>
               array('mysql:dbname=MyDB;host=10.1.2.7',
                     'mysql:dbname=MyDB;host=10.1.2.8',
                     'mysql:dbname=MyDB;host=10.1.2.9');
           );
       public static function getConnection($pool) {
           $max = count(self::$cfg[$pool]) - 1;
           $dsn = self::$cfg[$pool][mt_rand(0, $max)];
           return new PDO($dsn, USER, PASS);
       }
   }
   $db = DB::getConnection('read');