nodejs connection pool usage

Node.js is a front-end development language based on JavaScript. It provides very powerful capabilities for building real-time applications, can quickly respond to requests, and can support many development patterns (such as OO, functional programming, etc.). The non-blocking I/O feature of Node.js gives it ultra-fast performance, making it one of the most popular development languages ​​in recent years. However, when developing with Node.js, you also need to consider how to manage and connect to the database. In database operations, we usually encounter some problems, such as database connection pool management issues. Therefore, let's introduce the usage of Node.js connection pool.

1. What is a database connection pool?

When making a database connection, you may encounter the following problems:

1. Each connection needs to establish a new connection with the database. network connection, and establishing a network connection takes time and will affect the performance of the program.

2. If the program needs to frequently open and close the database, it will occupy database resources. If the website traffic is heavy, the database may be directly brought down.

3. Since connections are relatively expensive resources, under high concurrency conditions, requesting multiple connections at one time may cause memory to be exhausted.

To address these problems, we can use the database connection pool to solve them. The connection pool is like a cache pool. A set of database connections can be established in advance and placed in the pool. Every time the program needs a connection, it will be obtained from the connection pool and returned to the pool after use. This can effectively save time and resources, reducing network requests and server overhead.

2. Use of Node.js connection pool

Before using Node.js connection pool, you need to introduce npm’s famous MySQL module. The Node.js MySQL module is a very useful MySQL database connection library. It provides the Connection class, Pool class and PoolCluster class to realize connection and interaction with the MySQL database.

First, we need to install and introduce the MySQL module in Node.js:

npm install mysql

const mysql = require('mysql');

2.1 Establishing a connection pool

According to business needs, we can establish different numbers of connection pools, for example, establish a connection pool with a maximum number of connections of 10 and a minimum number of connections of 2. When the database cannot provide new connections, the program will report an error after waiting for a period of time. The code is as follows:

const pool = mysql.createPool({
host: '127.0.0.1',
user: 'root',
password: 'password',
database : 'mydb',
connectionLimit: 10,
queueLimit: 2
});

2.2 Get the connection from the connection pool

Establish the connection pool Finally, the program needs to obtain a connection from the connection pool to perform the operation. In the MySQL module, we use the getConnection method to get the connection from the connection pool.

pool.getConnection(function(err, connection) {

if (err) throw err;
console.log("连接成功！");

});

If the connection is successful, we can perform database operations through the connection object, such as querying the database The data. After completing the business requirements, the program needs to return the connection to the connection pool so that other functions or users can continue database operations. Use the release method to release the connection resources back to the connection pool. The code is as follows:

pool.getConnection(function(err, connection) {

if (err) throw err;
console.log("连接成功！");
connection.query('SELECT * FROM table1', function (error, results, fields) {
  // ... do something here with the results ... 
  connection.release();
});

});

3. Release of the connection pool

In actual During the application process, we need to pay attention to the release rules of the connection pool. If the connections in the connection pool are not released, a large amount of storage and memory resources will be occupied, causing the application to crash. Therefore, we need to release the connections in the connection pool in time.

For example, in the Express.js framework, we can use the app.on('close', callback) method to close the application and release all connection pool connections there. The code is as follows:

app.on('close', function(err) {
pool.end(function (err) {

if (err) throw err;
console.log("数据库连接池已关闭！");

});
});

4. Summary

The use of Node.js connection pool can help us manage database connections efficiently, improve program performance, and reduce resource overhead and security risks. In actual applications, corresponding configurations and adjustments need to be made according to business needs and system type to achieve optimal performance.

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