strace is returning a lot of open("/etc/hosts", O_RDONLY|O_CLOEXEC) for a php file

Question

I'm trying to debug why a PHP of mine is using so much of the CPU.

After running strace like this:

strace -e open,close php /scripName.php

It shows me all of the files that it uses and when I think it reaches the part of the code where it uses a MySql connection, it returns this:

open("/etc/host.conf", O_RDONLY|O_CLOEXEC) = 3
close(3)                                = 0
open("/etc/resolv.conf", O_RDONLY|O_CLOEXEC) = 3
close(3)                                = 0
open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 3
close(3)                                = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
close(3)                                = 0
open("/lib/i386-linux-gnu/libnss_dns.so.2", O_RDONLY|O_CLOEXEC) = 3
close(3)                                = 0
open("/etc/resolv.conf", O_RDONLY|O_CLOEXEC) = 3
close(3)                                = 0
close(3)                                = 0
open("/usr/share/mysql/charsets/Index.xml", O_RDONLY|O_LARGEFILE) = 4
close(4)                                = 0
close(3)                                = 0
open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 3
close(3)                                = 0
close(3)                                = 0
close(3)                                = 0
open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 3
close(3)                                = 0
close(3)                                = 0
close(3)                                = 0
open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 3
close(3)                                = 0
close(3)                                = 0
close(3)                                = 0
open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 3
close(3)                                = 0
close(3)                                = 0
close(3)                                = 0

and a LOT more of those

open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 3
close(3)                                = 0
close(3)                                = 0
close(3)                                = 0

each one taking quite a bit of time actually.

I tried pinpointing the problem by commenting lines until this didn't happen anymore, and I reached this class:

<?php
include_once 'config.php';

class db extends PDO {      
    public $dbtipo = DBTIPO;
    public $host = DBHOST;
    public $user = DBUSER;
    public $pass= DBPASS;
    public $db = DBNAME;

    function __construct(){
        $dns = $this->dbtipo.':host='.$this->host.";dbname=".$this->db;
        parent::__construct( $dns, $this->user, $this->pass ,
            array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES utf8"));
    }
}
?>

if I comment this line:

parent::__construct( $dns, $this->user, $this->pass ,
            array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES utf8"));

Then this doesn't happen anymore.

FYI, this class is used in another one like this:

public function getDataFromDb(){
    $connection = new db();
    $query = $connection->prepare("SELECT * FROM table");
    $query->execute();
    return $query;
}

The constants are defined in the config.php file as this:

define('DBTIPO', 'mysql');
define('DBHOST', 'mysite.com');
define('DBUSER', 'user');
define('DBPASS', 'password');
define('DBNAME', 'database_name');

Any ideas?

Answer 1

The host needs to resolve mysite.com to an IP address, so it looks in /etc/hosts where it presumably doesn't find it and then checks /etc/resolv.conf for the name servers to use for resolution and then presumably issues a DNS query to one of those name servers.

Depends on the desired operation, but if the MySQL server is on the same host then use localhost. If not then maybe add it to the hosts file.

Not sure how this relates to the CPU utilization, but answers the hosts and resolv.conf question.