Redis publish subscription

What is it?

Redis Publish subscribe （pub/sub） It's a message communication mode ： sender （pub） Release the news , subscriber （sub） receive messages .

Redis Clients can subscribe to any number of channels

subscribe / Release message map ：

The picture below shows the channel channel1, And three clients that subscribe to this channel ----client2,client5 and client1 The relationship between ：

        When new news passes PUBLISH Command to channel channel1 when , This message will be sent to the three clients who subscribe to it ：

command  

These comments are widely used to build instant messaging applications , Such as Internet chat room （chatroom） And real-time broadcasting , Real time reminder, etc

test  

The following example demonstrates how a publish subscription works , In our example, we create a subscription channel named redischat;

127.0.0.1:6379> subscribe redischat
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "redischat"
3) (integer) 1

Now? , Let's restart one first reids client , And then on the same channel redischat Two news releases , Subscribers can receive messages

127.0.0.1:6379> publish redischat hello,wyt
(integer) 1
127.0.0.1:6379> publish redischat hello,redis
(integer) 1
 

# The subscriber's client will display the following message

1) "message"
2) "redischat"
3) "hello,wyt"
1) "message"
2) "redischat"
3) "hello,redis"

principle

Redis It's using C Realized , Through analysis Redis Source code pubsub.c file , Understand the underlying implementation of publish and subscribe mechanisms , In order to deepen the understanding of Redis The understanding of the

Redis adopt PUBSLISH、SUBSCRIBE and PSUBSCRIBE And so on to realize the function of publish and subscribe

adopt SUBSCRIBE After subscribing to a channel ,reids-server It maintains a dictionary , The key of the dictionary is one by one chnnel, The value of a dictionary is a linked list , The linked list holds all the subscriptions channel The client of ,SUBSCRIBE The key to command , Is to add the client to the given channel In the subscription list of .

adopt PUBLISH Command to send messages to subscribers ,redis-server The given channel is used as the key , In what it maintains channel Look up the list of all clients who subscribe to this channel in the dictionary , Traverse the list , Publish the message to all subscribers

Pub/Sub Literally, it's publishing （Publish） With subscription （Subscribe）, stay Redis in , You can set to a certain key Value for message publishing and message subscription , When one key After the news is released on the value , All clients that subscribe to it will receive the corresponding message , The most obvious use of this feature is as a real-time messaging system , For example, ordinary instant chat , Group chat and other functions

Use scenarios

Pub/Sub Building a real-time messaging system

Redis Of Pub/Sub The system can build a real-time message system

For example, many uses Pub/Sub An example of real-time chat system