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This article mainly explains "how to use publish, subscribe and transaction in Redis". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let Xiaobian take you to learn "how to use publish, subscribe and transaction in Redis"!

publish-subscribe

Redis 'publish-subscribe system is somewhat similar to our radio stations, which can send broadcasts on one frequency, while we can receive broadcasts on any frequency. Broadcast in Android is similar to this.

Subscribe to messages as follows:

127.0.0.1:6379> SUBSCRIBE c1 c2 c3Reading messages... (press Ctrl-C to quit)1) "subscribe"2) "c1"3) (integer) 11) "subscribe"2) "c2"3) (integer) 21) "subscribe"2) "c3"3) (integer) 3

This means receiving messages from the three channels c1, c2, and c3. The way to send messages is as follows:

127.0.0.1:6379> PUBLISH c1 "hello redis! "(integer) 1

When a message is sent on channel c1, you can see the following output in the message subscription console:

1) "message"2) "c1"3) "hello redis! "

In redis, we can also use pattern-matching subscriptions, as follows:

127.0.0.1:6379> PSUBSCRIBE c*Reading messages... (press Ctrl-C to quit)1) "psubscribe"2) "c*"3) (integer) 1

At this time, all messages from channels starting with c can be received.

tips

The publish-subscribe system in redis is still very useful in some scenarios, but there are some problems to be aware of: because the network may encounter unexpected situations such as disconnection during transmission, it needs to be reconnected after disconnection, but this will cause data loss during disconnection.

Affairs

Since redis is a NoSQL database, it certainly has transactional capabilities, but the transactions here are slightly different from those in our relational databases.

The usage of transactions in redis is very simple. We start a transaction with MULTI command, as follows:

127.0.0.1:6379> MULTIOK

After the MULTI command is executed, we can continue to send commands to be executed. In this case, the commands will not be executed immediately, but will be placed in a queue, as follows:

127.0.0.1:6379> set k1 v1QUEUED127.0.0.1:6379> set k2 v2QUEUED127.0.0.1:6379> set k3 v3QUEUED

When all the commands are entered, we can initiate execution through EXEC command, or we can clear the queue through DISCARD command, as follows:

127.0.0.1: 6379> EXEC1) OK2) OK3) OK Exception in transaction

Exceptions to transactions in redis fall into two general categories:

1. Errors that can be detected before entering the queue, such as incorrect command input;

2. Errors that cannot be detected until EXEC is performed, such as adding 1 to a non-numeric character;

So redis has different handling strategies for these two different exceptions. For the first error, the server records the failure of the command enqueue, and refuses to execute and automatically abandons the transaction when the client calls the EXEC command (this is the version practice after 2.6.5, and the previous version practice can refer to the official documentation). As follows:

127.0.0.1:6379> MULTIOK127.0.0.1:6379> set kv1 v1QUEUED127.0.0.1:6379> set k2 v2QUEUED127.0.0.1:6379> set k3 v3 3 3QUEUED127.0.0.1:6379> set k4 v4QUEUED127.0.0.1:6379> EXEC1) OK2) OK3) (error) ERR syntax error4) OK127.0.0.1:6379> keys *1) "k4"2) "k2"3) "kv1"

In the second case, redis doesn't treat them specially, and even if one or some of the commands in the transaction generates an error, the other commands in the transaction continue to execute. As follows:

127.0.0.1:6379> MULTIOK127.0.0.1:6379> set k1 vvQUEUED127.0.0.1:6379> INCR k1QUEUED127.0.0.1:6379> EXEC1) OK2) (error) ERR value is not an integer or out of range127.0.0.1:6379> GET k1"vv"

Unlike relational databases, transactions in redis do not roll back when they go wrong. The official explanation for this is as follows:

Redis commands only fail because of incorrect syntax (and these problems cannot be detected at enqueue time), or because the command is used on the wrong type of key: that is, from a practical point of view, the failed command is caused by programming errors that should be detected during development, not in production. Because there is no need to support rollback, the internals of Redis can be kept simple and fast. WATCH command

The WATCH command in a transaction can be used to monitor a key, and through this monitoring, we can provide (CAS) behavior for redis transactions. If at least one WATCH key is modified before EXEC executes, the entire transaction is canceled and EXEC returns nil-reply to indicate that the transaction has failed. As follows:

With the unwatch command, you can cancel the monitoring of a key, as follows:

At this point, I believe everyone has a deeper understanding of "how to use publish, subscribe and transaction in Redis". Let's do it in practice! Here is the website, more related content can enter the relevant channels for inquiry, pay attention to us, continue to learn!

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