PHP & MySQL Warning: mysqli_connect() [function.mysqli-connect]: (HY000/2005): Unknown MySQL server host

Okay when I go to my web page I get the following error below but when I reload the page everything is okay and is displayed fine. What exactly is the problem and how can I fix it?

ERROR.

Warning: mysqli_connect() 开发者_StackOverflow中文版[function.mysqli-connect]: (HY000/2005): Unknown MySQL server host

MySQL code.

$mysqli = mysqli_connect("example.com", "avd", "password", "avd");

Server/Port combination is invalid, can't be resolved, or port is bad.