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Dokumen ini menggunakan Manual laman web PHP Cina Lepaskan
(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
$
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() 。
[#1] Doug [2010-04-19 08:24:45]
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.
[#2] alext at marketdream dot com dot mx [2009-09-29 08:28:10]
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.
[#3] luky37 [2009-02-03 11:15:09]
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).
[#4] miro dot dietiker at md-systems dot ch [2007-08-31 11:32:24]
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...
[#5] dustin hawkins [2006-07-31 12:32:47]
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....
?>
[#6] cybot2000 at yahoo dot de [2005-05-25 16:44:23]
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.
[#7] vinicius at teracom dot com dot br [2004-03-16 07:35:00]
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.