What are the Performance and Scalability characteristics of MySQL?What is difference between mysql_connect and mysql_pconnect?
From the manual (http://php.net/mysql_pconnect) :
mysql_pconnect() acts very much like mysql_connect() with two major differences.
First, when connecting, the function would first try to find a (persistent) link that’s already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection.
Second, the connection to the SQL server will not be closed when the execution of the script ends. Instead, the link will remain open for future use (mysql_close() will not close links established by mysql_pconnect()).
This type of link is therefore called ‘persistent’.
And you shouldn’t use either. From the same page:
This extension is deprecated as of PHP 5.5.0, and will be removed in the future. Instead, the MySQLi or PDO_MySQL extension should be used
guido is correct. My concern is your use of “thread”. Do you mind giving us a use case? PHP itself doesn’t really have great support for multi threading.