How to correctly close MySQL connection pool connections and resources in a PHP program?

How to correctly close the connections and resources of the MySQL connection pool in a PHP program?

When developing PHP programs, we often need to interact with the database, and MySQL is a very common relational database. In PHP, we can use the MySQL connection pool to manage connections to the database to improve program performance and efficiency. However, in the process of using the connection pool, we need to pay attention to closing the connection and releasing resources correctly to avoid problems.

First, we need to understand how connection pooling works. The connection pool is a mechanism for maintaining and managing connections. When the program needs to connect to the database, it can obtain the established connection from the connection pool without re-establishing the connection. When using a connection pool, a maximum number of connections is usually set. When the number of connections reaches the maximum, new connection requests will be temporarily blocked or rejected. The connection pool will maintain a certain number of idle connections to quickly respond to database connection requests.

In PHP, we can use mysqli or PDO extension to connect and operate MySQL database. Regardless of which extension you use, the steps for closing a connection are similar. The following are some methods and principles for closing connections and releasing resources:

1. After using the database connection, the connection must be closed explicitly. This ensures that database connections are released promptly so that other programs or requests can continue to use them. For each connection, use the close() or disconnect() method provided by mysqli or the PDO extension to close the connection.
2. Before closing the connection, ensure that all database operations have been completed. This includes operations such as read, write, update, delete, etc. If there are unfinished operations before closing the connection, data loss or operation failure may result.
3. Avoid opening and closing connections in a loop. This will consume a lot of resources and affect the performance of the program. A connection can be created before the loop starts and closed at the end of the loop. If connections are opened and closed too frequently, consider using a connection pool mechanism to avoid opening and closing connections frequently.
4. If you are using a connection pool, ensure that the connection has been returned to the connection pool correctly. For the mysqli extension, the mysqli_close() method can be used to close the connection and automatically return it to the connection pool. For PDO extensions, just set the connection to null to close the connection and release the resources.
5. Avoid leaking connections and resources. When a connection is opened but not closed correctly, it will continue to occupy resources in the connection pool, causing the connection pool to be full and no new connections can be established. In order to avoid connection leakage, ensure that the connection is closed promptly after use and its corresponding resources are released.

In short, it is very important to correctly close the connections and resources of the MySQL connection pool in the PHP program. Following the above principles and methods can help us avoid connection leaks, resource waste and performance problems. Properly closing connections and releasing resources will make our programs more robust, efficient, and stable.

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