优雅的Redis轮询取数据之旅（redis轮询取数据）

Our Redis polling journey is often a surprise. I’d like to share it with you today.

Redis is an in-memory key-value store, often used as a database, cache and message broker. In some cases we may need to facilitate a “long poll” or persistent connection between a Redis server and a web server or application.

In this case, Redis comes to the rescue. Redis can be used to implement a polling system that can detect changes to the database almost in real-time, without involving client-side refreshes.

Let’s dive into some code in order to understand how this works. We’ll first need to set up a basic Redis client. We’ll use the Node.js Redis library for this, so our code will be in JavaScript.

const redis = require(‘redis’);

const client = redis.createClient();

Then we define a function which will be responsible for listening for changes in Redis.

function watchDB() {

let time = Date.now();

console.log(`Listening for changes since ${time}`);

// Start a Redis “stream” connection

let stream = client.xread(‘STREAMS’, ‘my-stream’, time, ‘COUNT’, 10);

// Return the stream’s data

return stream.then(data => {

// The data variable is an array,

// so we loop through it

data.forEach(stream => {

let key = stream[0];

let entries = stream[1];

// Now we loop through the entries

entries.forEach(entry => {

let id = entry[0];

let values = entry[1];

// Here we process each entry to

// get the item that was added

let item = values[1];

// Finally, we can evaluate it

console.log(`Item “${item}” added to stream`);

});

});

// After we process each entry,

// we call the watchDB() function agn.

watchDB();

});

}

Finally, we’ll start the function.

watchDB();

And that’s it! You now have a basic system in place that will detect changes to your Redis data in real-time. Thanks to Redis’ powerful stream feature, you can now rest easy knowing that your application and web servers will never miss any critical updates.