Redis has become the standard cache for Internet companies due to its excellent features of high performance and lightweight. Sometimes we want to add some custom commands, mainly in scenarios where Redis is heavily used. , like rush buying scenarios, it is necessary to ensure the transactionality of multiple Redis commands. If there is no good atomicity guarantee, data inconsistency problems may easily occur.

Although the official transaction plan is given, if it is necessary to make a judgment based on the return value of a certain command before proceeding to the next step, the transaction plan will not be able to cope with it.

Today we will use a practical case to describe how to add a Redis command. This command is mainly used in anti-swipe scenarios:

It is often necessary to ban a certain IP or a certain user for a period of time. If this command is not used, the solution is as follows:

First incr, and then determine whether it is 1. If it is 1, set the expiration time. It can be seen that if the first client that initiates the incr request hangs up during high concurrency, the key will not expire.

The command to be written today is used to ensure this transaction. The server side ensures that if the value of the key is 1, the expiration time is set.

The command usage is as follows:

incexpire key expireTime maxNum

key: the key to be processed

expireTime: expiration time, in seconds. If you write 10, it means that the key will expire in 10 seconds. ;

maxNum: Indicates the amount to which it will increase until it stops increasing. If it is set to 10, the maximum value returned is 11. Returning 11 means it has been exceeded;

2. Writing commands

1. Download the redis code

The Redis version used in this article is 3.2.11;

Download the code and cut to the 3.2.11 branch

git clone https://github.com/antirez/redis

2.Writing and adding Command code

1) Add a new command to the redisCommandTable structure in src/server.c

struct redisCommand redisCommandTable[] = {

redisCommandTable is an array, each item represents a redis command, and the first one represents a command The second one is the actual processing function, and the third one is the number of parameters. The others will not be discussed in detail.

2) Add a function declaration in src/server.h:

void incrExpireCommand(client *c);

3) Then add a file as ljh.c (name it yourself) and add the following code:

#include "server.h"

4) Add a new file ljh.o in src/Makefile

REDIS_SERVER_OBJ=adlist.o quicklist.o ae.o anet.o dict.o server.o sds.o zmalloc.o lzf_c.o lzf_d.o pqsort.o zipmap.o sha1.o ziplist.o release.o networking

The execution effect is as follows

You can see that after key1 is increased to 11 It no longer increases, and after 10 seconds, it becomes 1 again.

Finally, we still have to ask ourselves whether it is necessary to add Redis commands in our scenario. If necessary, we must grasp the responsibilities between each layer and do not let Redis end up processing business; generally It is said that the middleware layer generally handles more general functions. The lower layers should be more stable and the less changes are, the normal situation is.

For more related knowledge, please pay attention to redis introductory tutorialcolumn

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