PHP-MySQLi connection randomly fails with "Cannot assign requested address"

Question

Since about 2 weeks I'm dealing with one of the weirdest problems in LAMP stack. Long story short randomly connection to MySQL server is failing with error message:

Warning:  mysqli::real_connect(): (HY000/2002): Cannot assign requested address in ..

The MySQL is on different "box", hosted at Rackspace Cloud Today we downgraded it's version to

Ver 14.14 Distrib 5.1.42, for debian-linux-gnu (x86_64).

The DB server is pretty busy dealing with Queries per second avg: 5327.957 according to it's status variable.

MySQL is in log-warnings=9 but no warring for connection refused are logged. Both site and gearman workers scripts fail with that error at let's say 1% probability. No server load DO NOT seems to be a factor as we monitor. (CPU load, IO load or MySQL load) The maximum DB connections (max_connections) are setted to 200 but we have never dealed with more than 100 simultaneous connections to the database

It happens with and without the firewall software.

I suspect TCP Networking problem rather than PHP/MySQL configurationn problem.

Can anyone give me clue how to find it?

UPDATE:

The connection code is:

$this->_mysqli = mysqli_init(); 
$this->_mysqli->options(MYSQLI_OPT_CONNECT_TIMEOUT, 120); 
$this->_mysqli->real_connect($dbHost,$dbUserName, $dbPassword, $dbName); 

if (!is_null($this->_mysqli->connect_error)) {
    $ping = $this->_mysqli->ping(); 

    if(!$ping){
        $error = 'HOST: {'.$dbHost.'};MESSAGE: '. $this->_mysqli->connect_error ."\n"; 
        DataStoreException::raiseHostUnreachable($error);
    }
} 

Answer 1

I had this problem and solved it using persistent connection mode, which can be activated in mysqli by pre-fixing the database hostname with a 'p:'

$link = mysqli_connect('p:localhost', 'fake_user', 'my_password', 'my_db');

From: http://php.net/manual/en/mysqli.persistconns.php :

The idea behind persistent connections is that a connection between a client process and a database can be reused by a client process, rather than being created and destroyed multiple times. This reduces the overhead of creating fresh connections every time one is required, as unused connections are cached and ready to be reused. ...

To open a persistent connection you must prepend p: to the hostname when connecting.