Php内存回收

最近在写一个从mysql导数据到memcache的php cli脚本，每次执行内存都一直上涨，内存没有回收，经过一晚的debug，终于在unset了以后释放了内存

private static function updateGlCache($field, $value, $tabname, $mem) {
    $cache_key = get_cache_key("gl_{$field}", $value);
    $tabnames = $mem->get($cache_key);

    if($tabnames == null) {
        $mem->set($cache_key, array($tabname));
        print_r("flushing:{$field}{$value}{$tabname}\n");
    }else {
        if(!in_array($tabname, $tabnames)) {
            array_push($tabnames, $tabname);
            $mem->set($cache_key, $tabnames);
            print_r("flushing:{$field}{$value}{$tabname}\n");
        }
    }

    unset($tabnames); //gc
    unset($cache_key); //gc
}