Detailed explanation of the difference between mysql_connect and mysql_pconncet in PHP_PHP tutorial

Let’s talk about the difference between mysql_connect and mysql_pconnect . The usage of these two functions is similar. Some people on the Internet say that pconnect should be used. Ambiguous. So what is this thing like?

A permanent link does not mean that the server opens a connection and then everyone shares the link. Permanent connections also open a connection for each client. If 200 people visit, there will be 200 connections. In fact, mysql_pconnect() itself does not do much processing. The only thing it does is not to actively close the mysql connection after PHP is running.

When PHP is run in cgi mode, pconnect and connect are basically absent. The difference is that in the cgi method, each PHP access starts a process. After the access is completed, the process ends and all resources are released. When PHP is run in the apache module mode, since apache uses a process pool, an httpd process ends. After that, it will be put back into the process pool, which means that the mysql connection resource opened with pconnect will not be released, so it can be reused when there is the next connection request. This makes it possible to use Apache when the concurrent access volume 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 easier to understand. However, when the concurrent access volume of apache is large, if pconnect is used, it will be occupied by some previous httpd processes. If the mysql connection is not closed, it may be that mysql has reached the maximum number of connections, so that some subsequent requests will never be satisfied. If the maximum number of mysql connections is set to 500, and the maximum number of simultaneous accesses of apache is set to 2000, assuming that all Access will require access to the db, and the operation time will be relatively long. When the current 500 httpd requests are not completed, subsequent httd processes will not be able to connect to mysql (because the maximum number of mysql connections has been reached). Only the current 500 Mysql can be connected only after the httpd process ends or is reused.

When the db operation is complex and takes a long time, httpd will fork many concurrent processes, and the httpd process generated first will not release the db connection. , making the later httpd process unable to connect to the db. Because the mysql connections of other httpd processes are not reused, many connection timeouts will occur. When the number of concurrent visits 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.

In my personal opinion, PHP now The 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, using mysql_pconnect, each refresh and requesting a new page is faster, while using mysql_connect, each refresh must be re-requested. When the database connection is slow, the difference can be seen. . 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.

pconnect does not need to be closed 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. One sentence summary: To make good use of pconnect, it is not only a matter of php scripts, but also related to the settings of the database and server.