Codeigniter Hook Db Log

Db_log.php

<?php
class Db_log{
	public function queries(){
		$CI = &get_instance();
		$filename = APPPATH."logs/queries-".date("Y-m-d").".php";
		$queries = $CI->db->queries;
		$times = $CI->db->query_times;
		foreach($queries as $k => $v){
			$queries[$k] = date("Y-m-d H:i:s")." - ".$times[$k]." : "."$v;\n";
		}
		$queries = implode("",$queries );
		file_put_contents($filename, $queries, FILE_APPEND);
	}
}

hooks.php

$hook['post_controller'] = array(
	'class' => "Db_log", 
	'function' => "queries", 
	'filename' => "Db_log.php", 
	'filepath' => "hooks"
);