[summary of interview questions] zj6 redis

redis Common commands

What are various data types commonly used for

String: Can be used for caching 、 Distributed Session

Hash： Can be used to store user information 、 User home page visits 、 Combination query
（hash Better for storing objects , Store an object in hash Type will take up less memory , And easy access to the entire object .）
hmset myhash field1 value1 field2 value2： Set up multiple field

List： Timeline list of Weibo followers , Simple queue
Set： Fabulous 、 Step on 、 Friend relationship （ You can find intersection union difference sets ）
Zset： Ranking List

exists key Judge whether it exists key
expire key 10 10s Be overdue

redis General Command
Redis Operation command summary

redis Save a decimal 1.5 How to add one

incrbyfloat Add or subtract floating point numbers
Be careful ：incr Is integer increment

redis If it exists, operate the command

set key value Just insert when it doesn't exist , exist iju Modify .

Be careful ：
setnx key value If it does not exist, perform the operation , There is no operation
setex key time value Set expiration time （expire）

redis Message queue of list aggregate , How do producers and consumers know if there is any news inside

Redis Of List The main operations of are lpush/lpop/rpush/rpop Four kinds of , From the head and from the tail push/pop, besides List There are also two pop Blocking version of the operation blpop/brpop, Used to block getting an object （list When there is no data hi Blocked ）.

Redis It is usually used as a message server to handle background work or message tasks . A simple queue mode ： The producer puts the message into a list , Consumers waiting for news use rpop command （ By polling ）, Or use brpop To get the news .

In order to prevent data loss and inconsistency （ That is, the consumer just took out the message and collapsed , Message not processed ）, use rpoplpush command ： Not only does it return a message, it also adds the message to another backup list , If everything goes well , After the client finishes processing the message , use rem Delete the corresponding message from this sub table . If it fails, the message will be bounced back from the backup table to the original queue rpoplpush
Java Jedis operation Redis Example （ Two ）——list producer / The consumer pattern implements message queuing