mysql_ping()

(PHP 4 >= 4.3.0, PHP 5)

Ping 一个服务器连接，如果没有连接则重新连接

说明

mysql_ping([resource$ link_identifier]): bool

mysql_ping()检查到服务器的连接是否正常。如果断开，则自动尝试连接。本函数可用于空闲很久的脚本来检查服务器是否关闭了连接，如果有必要则重新连接上。如果到服务器的连接可用则mysql_ping()返回TRUE，否则返回FALSE。

参见mysql_thread_id()和mysql_list_processes()。

It should be noted that mysql_ping() seems to reset the error message on the server.
I used it to check whether the connection was still alive before reading the error message via mysql_error() and it always returned an empty string. Upon removing the connection check everything worked.

mysql_ping() is really helpful when you have this annoying error:
MYSQL Error 2006 Server has gone away
For CI users:
In 1.7.2 version of codeigniter, there is a function 
$this->db->reconnect() 
that uses mysql_ping() to reestablish the timed out connection.
This function is specially useful when developing social media sites that uses hundreds of connections to the db such asinserting or selecting.

This function *does not* attempt to reconnect at this time. It only tells you whether or not you currently *are* connected.
To actually reconnect, you will have to implement this yourself in a wrapper class.

When using the mysql_ping command under php 5.1.2 and mysql 5.0, I was having problems with the auto-reconnect "feature", mainly that when the connection was severed, a mysql_ping would not automatically re-establish the connection to the database.
The connection to the DB is dropped when the time without a query excedes the wait_timeout value in my.cnf. You can check your wait_timeout by running the query "SHOW VARIABLES;"
If you're having problems auto-reconnecting when the connection is dropped, use this code:
<?php
$conn = mysql_connect('localhost','user','pass');
mysql_select_db('db',$conn);
if (!mysql_ping ($conn)) {
  //here is the major trick, you have to close the connection (even though its not currently working) for it to recreate properly.
  mysql_close($conn);
  $conn = mysql_connect('localhost','user','pass');
  mysql_select_db('db',$conn);
}
//run queries knowing that your connection is alive....
?>

When checking if a $resource works...
be prepared that mysql_ping returns NULL as long as $resource is no correct mysql resource.
<?php
$resource =NULL;
var_dump = @mysql_ping($resource);
# showing NULL
?>
This could be used to decide of a current $resource is a mysql or a mysqli connection when nothing else is available to do that...

Is important to remember that if your first connection to mysql don't works, mysql_ping will always return true! So, if you want to check if mysql is connected, first of all you must check if mysql_connect do not returns false and then you can begin to check mysql_ping.

If you get 'error 2006: MySQL server has gone away' messages when running (really) long scripts, mysql_ping will help detecting the loss of the db-connection. This can happen, when 'wait timeout' is reached (MySQL default is 8 hours).