MySql和ADODB5 - 最大连接数

Question

Here's an example of php code to make a connection to mysql and perform a select query using adodb :

include('adodb.inc.php');    # load code common to ADOdb
$db = &ADONewConnection('mysql'); 
$db->PConnect("localhost", "root", "password", "database");
$recordSet = &$conn->Execute('select * from products');
if (!$recordSet) 
         print $conn->ErrorMsg();
else
while (!$recordSet->EOF) {
         print $recordSet->fields[0].' '.$recordSet->fields[1].'<BR>';
         $recordSet->MoveNext();
}

$recordSet->Close(); # optional
$conn->Close(); # optional
?>

Do i have to use

$db = &ADONewConnection('mysql'); 
$db->PConnect("localhost", "root", "password", "database");

and

$recordSet->Close(); # optional
$conn->Close(); # optional

each time i want to make a query to unsure the error of max_connection reached ?

How can i manage when 1000 users or more are connected to my website with MySQL's max_connection = 100 ?

Answer 1

When the maximum number of connections has been reached, your $db->PConnect should throw an exception or return an error code (I don't know this driver too much, please check the man pages). You must watch this error and act accordingly in case of error. Typically, wait a few seconds, and try again a couple of times before returning an error to the user.

Now, the max_connection is the limit of concurrent connections. 1000 users connected to your application are (hopefully) not all running a query at the same time, so you should be safe for a while. At the end of a script execution, all connections are closed (or returned to the pool in your case), and become available to other users. So you will not reach your limit of 100 unless 100 users are actually clicking at the same time on some link in your application.

But you should write your scripts so that they open (or acquire) a connection as late as possible during the course of their execution, and close (or release) the connection as early as possible. This way, the connection is held for a span of time as short as possible, making it less likely to hit the limit.

Now, if you do reach the limit, then there is nothing else you can do but increasing the limit. The only workaround is to put exceeding connection requests on hold (as I suggest in the first paragraph).