The difference in usage between mysql_connect and mysql_pconncet in php

Permanent connections also open a connection for each client. If 200 people visit, there will be 200 connections. mysql_pconnect() itself does not do much processing, the only thing it does is not to actively close the mysql connection after php is finished running.

When PHP is run in cgi mode, there is basically no difference between pconnect and connect, because in cgi mode, each PHP access starts a process. After the access is completed, the process ends and all resources are released. When php is running in the apache module mode, since apache uses a process pool, an httpd process will be put back into the process pool after it ends. This also prevents the mysql connection resource opened with pconnect from being released, so there is a next connection. It can be reused when requested. This means that when the concurrent access of Apache is not large, due to the use of pconnect, PHP saves the time of repeatedly connecting to the db, making the access speed faster. This should be relatively easy to understand. But in When apache has a large amount of concurrent access, if you use pconnect, some of the mysql connections occupied by some previous httpd processes are not closed, and some subsequent requests may never be satisfied because mysql has reached the maximum connection. If mysql The maximum number of connections is set to 500, and the maximum number of simultaneous accesses of Apache is set to 2000. It is assumed that all accesses will require access to the db, and the operation time will be relatively long. When the httpd of the current 500 requests has not ended, the subsequent httpd process will It is impossible to connect to mysql (because the maximum number of mysql connections has been reached). Only when the current 500 httpd processes end or are reused can I connect to mysql.

When the db operation is complex and takes a long time, httpd will fork many concurrent processes, and the httpd process generated first does not release the db connection, so that the httpd process generated later cannot connect to the db. This is because other httpd processes are not reused. MySQL connection of the process. As a result, many connection timeouts will occur. When the amount of concurrent access is not high, using pconnect can simply improve the access speed, but after the amount of concurrency increases, whether to use pconnect again depends on the programmer's choice.

PHP’s current connection to MySQL does not really use the connection pool. pconnect is just equivalent to borrowing the process pool of apache, so pconnect cannot improve the efficiency of accessing the db when the amount of concurrent access is large.

In actual applications, if you use mysql_pconnect, each refresh and request for a new page will be faster, while if you use mysql_connect, you will need to re-request each refresh. When the database connection is slow, you can see the difference. . When your database connection is slow, the DB operation is not very complicated, and your program is confident enough that it will not cause deadlock, or you have control over the server and meet any two of the above four conditions, then You can use pconnect.

You don’t need to close pconnect in the script. You can set the lifetime in mysql, or you can write a shell to scan regularly and kill connections that have been dormant for too long. Summary: To use pconnect well, you must consider the high quality of the PHP code and the configuration of the server and site.