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【Redis series 】 Redis learn nine, Redis publish and subscribe how to play
Redis publishes subscriptions
Redis publish subscription (PUB/SUB) is a message communication mode
- The sender sends the message PUB
- The receiver subscribes to the message sub
For example, wechat, Weibo and other attention systems
Redis clients can subscribe to any number of channels without limit
So let’s look at the diagram
- Message publisher
- Message subscribers
- channel
In this case, the message publisher and the message subscriber are both Redis clients, the subscriber subscribs to a channel, the publisher publishes relevant information in the channel, such as articles, such as boiling points, etc., and the message subscriber can receive the content just sent by the publisher in real time
In the image below, channel Channel1
And the relationship between the three clients that subscribe to this channel — Client2, Client5, and client1:
When a new message is sent to channel Channel1 via PUBLISH
This message is sent to the three clients that subscribe to it:
Common commands
The following table lists the common redis publish and subscribe commands:
| The serial number | Commands and Description |
|---|---|
| 1 | PSUBSCRIBE pattern [pattern …] Subscribe to one or more channels that conform to a given pattern. |
| 2 | PUBSUB subcommand [argument [argument …] View the subscription and publication system status. |
| 3 | PUBLISH channel message Sends the message to the specified channel. |
| 4 | [PUNSUBSCRIBE [pattern [pattern …] Unsubscribe all channels for a given mode. |
| 5 | SUBSCRIBE channel [channel …] Subscribe to a given channel or channels of information. |
| 6 | UNSUBSCRIBE [channel [channel …] To unsubscribe from a given channel. |
Actual testing and validation
- subscribe channel [channel …]
Subscribe to one or more channels
- PUBLISH channel message
Send a message to a channel
The receiver:
Subscribe xiaomotong channel, as long as the sender has a publish message to the channel, the receiver can immediately receive it
127.0.0.1:6379> subscribe xiaomotong
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "xiaomotong"
3) (integer) 1
1) "message"
2) "xiaomotong"
3) "hellowrold"
1) "message"
2) "xiaomotong"
3) "hello_redis"
1) "message"
2) "xiaomotong"
3) "xiaozhupeiqi"
Copy the codeThe sender:
The sender sends message, Hellowrold, hello_redis, xiaozhupeiqi to Xiaomotong channel in turn
root@iZuf66y3tuzn4wp3h02t7pZ:~# redis-cli
127.0.0.1:6379> publish xiaomotong hellowrold
(integer) 1
127.0.0.1:6379> publish xiaomotong hello_redis
(integer) 1
127.0.0.1:6379> publish xiaomotong xiaozhupeiqi
(integer) 1
Copy the codeSo how does this implementation work?
Realize the principle of
Redis is a single-process open source component implemented in C language
By analyzing the publish.c file in redis source code, we can understand the underlying implementation of Redis publish subscription, which can deepen our understanding of Redis
Redis implements publish and subscribe through commands such as publish, subscribe, and psubscribe
For example, wechat, which we all use:
subscribe
After subscribing to a channel, redis-server maintains a dictionary. The key of the dictionary is the name of the channel, and the value of the dictionary is a linked list of all clients that subscribe to the channel
A subscribe instruction adds a client to a channel’s subscription list
publish
Redis publishes messages to the channel. Redis server uses the given key as the channel name, keeps a list of all clients subscribing to the channel in the channel dictionary it maintains, traverses the list, and sends messages to all subscribers
pub / sub
Pub/sub: Publish and subscribe
In Redis, we can publish and subscribe messages to a certain key value. When a message is published on a key value, all clients subscribing to it will receive the message it just published. The most obvious use of this function is as a real-time messaging system
For example, we usually use chat system, instant messaging system and so on
But we need to be careful here
In order to realize the Redis cluster, all subscribed clients can receive published messages, but different clients may be connected to different master nodes, so Redis will broadcast all published messages to all nodes. If the published messages are large, the network overhead will be high, so it is necessary to avoid sending large messages
Redis publish/subscribe application scenario
1. Real-time messaging system
2, instant messaging, channel as a chat room, the message back to all subscribe to the channel
3, subscription system, concerned about the system is OK
For complex scenarios, forget about Redis and use professional MQ open source components such as rabbitMQ or Kafka
Points to note when using Redis to publish/subscribe
Publishing/subscribing using Redis is flawed
1. The reliability requirement for message processing is not strong
2. Consumption power does not need to be enhanced by increasing consumers
References:
redis_doc
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