protected function createCacheTable($db,$tableName)
	{
		$driver=$db->getDriverName();
		if($driver==='mysql')
			$blob='LONGBLOB';
		elseif($driver==='pgsql')
			$blob='BYTEA';
		else
			$blob='BLOB';
		$sql=<<<EOD
CREATE TABLE $tableName
(
	id CHAR(128) PRIMARY KEY,
	expire INTEGER,
	value $blob
)
EOD;
		$db->createCommand($sql)->execute();
	}