MySQL 函数
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PHP手册

mysql_ping

(PHP 4 >= 4.3.0, PHP 5)

mysql_ping — Ping 一个服务器连接，如果没有连接则重新连接

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()。

MySQL 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: Ping 一个服务器连接，如果没有连接则重新连接

用户评论:

Doug (19-Apr-2010 04:24)

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.

alext at marketdream dot com dot mx (29-Sep-2009 04:28)

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.

luky37 (03-Feb-2009 07:15)

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).

oscar at bitagenda dot com (02-Oct-2007 12:10)

Very confusing description.
... If it has gone down, an automatic reconnection is attempted
 (But the function returns only true or false, so if you have variable say $link = connection resource, it will be an invalid resource)

Then ...
... Note:  Since MySQL 5.0.13, automatic reconnection feature is disabled.

OK, if it returns false, I have the chance to reconnect updating my resource variable
$link = reconnect

But I did called the function with $link to do the check, so ...
If no such link is found, it will try to create one as if mysql_connect() was called with no arguments (this are  different arguments than automatic reconnection, doesn't it? I think, automatic reconnecting, say to $link, would be with its own arguments previously used to create the connection)

So bad decision about automatic recconection feature disabled ...

At least the function should have the param by reference, so in case it reconnects with a new link_identifier.

bool mysql_ping ( &[resource $link_identifier] )

Or a return value of link_identifier, not true.

if ($link=mysql_ping($link)) {...} else { whatever }

miro dot dietiker at md-systems dot ch (31-Aug-2007 07:32)

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...

dustin hawkins (31-Jul-2006 08:32)

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 12:44)

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 03:35)

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.