mysql_ping

说明

bool mysql_ping ( [resource link_identifier] )

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()。

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dustin hawkins
01-Aug-2006 03:32


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....



?>

cybot2000 at yahoo dot de
26-May-2005 07:44


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.

vinicius at teracom dot com dot br
16-Mar-2004 11:35


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.

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