There are five data structures in the redis database, which are: string-string, Hash-dictionary, List-list, Set-set, and Sorted Set-ordered set.
These five data structures have different usage scenarios. Let’s introduce their usage scenarios below.
1. String
String data structure is a simple Key-Value type. Value can be not only String, but also a number (when the number type can be represented by Long, the encoding is an integer type. , others are stored in sdshdr as strings). Using the String type, the current functions of Memcached can be fully realized and more efficient. You can also enjoy the scheduled persistence of redis (you can choose RDB mode or AOF mode), operation log and Replication and other functions. In addition to providing the same get, set, incr, decr and other operations as Memcached, redis also provides the following operations:
1.LEN niushuai：O(1)获取字符串长度 2.APPEND niushuai redis：往字符串 append 内容，而且采用智能分配内存（每次2倍） 3.设置和获取字符串的某一段内容 4.设置及获取字符串的某一位（bit） 5.批量设置一系列字符串的内容 6.原子计数器 7.GETSET 命令的妙用，请于清空旧值的同时设置一个新值，配合原子计数器使用
2, Hash
In Memcached, we often use some The structured information is packaged into a HashMap, which is serialized on the client and stored as a string value (usually in JSON format), such as the user's nickname, age, gender, etc. At this time, when you need to modify one of the items, you usually need to take out the string (JSON), then deserialize it, modify the value of a certain item, and then serialize it into a string (JSON) and store it back. Simply modifying an attribute to do so many things must be very expensive, and it is not suitable for some situations where concurrent operations are possible (for example, two concurrent operations need to modify the age). The Hash structure of redis allows you to modify only a certain attribute value just like updating an attribute in the database. (Storing, reading, and modifying user attributes)
3. List
List is simply a linked list (redis uses a double-ended linked list to implement List). I believe that anyone who has learned data structure knowledge will Its structure should be understood. Using the List structure, we can easily implement functions such as the latest news ranking (such as Sina Blog's TimeLine). Another application of List is the message queue. You can use the Push operation of List to store tasks in the List, and then the worker thread uses the PoP operation to take out the task for execution. Redis also provides an API for operating a certain segment of elements in the List. You can directly query and delete a certain segment of elements in the List.
(Learning video sharing: redis database tutorial)
4. Set
Set is a set. The concept of a set is a bunch of unique values. The combination. Some collective data can be stored using the Set data structure provided by Redis. For example, in the Weibo application, all the followers of a user can be stored in a collection, and all the fans can be stored in a collection. Because Redis is very user-friendly and provides operations such as intersection, union, and difference for collections, it is very convenient to implement functions such as common attention, common preferences, and second-degree friends. For all the above collection operations, you can also You can use different commands to choose whether to return the results to the client or save them in a new collection.
1.共同好友、二度好友 2.利用唯一性，可以统计访问网站的所有独立 IP 3.好友推荐的时候，根据 tag 求交集，大于某个 threshold 就可以推荐
5. Sorted Set
Compared with Set, Sorted Set adds a weight parameter score to the elements in the set, so that the elements in the set can be arranged in an orderly manner according to the score. For example, in a Sorted Set that stores the grades of the entire class, the set value can be the student ID number, and the score can be the test score. In this way, when the data is inserted into the set, natural sorting has already been performed. In addition, Sorted Set can also be used to create a weighted queue. For example, the score of ordinary messages is 1 and the score of important messages is 2. Then the worker thread can choose the reverse order of the sore to obtain the work tasks. Prioritize important tasks.
2. Usage scenarios of other redis functions
1. Subscription-publishing system
Pub/Sub literally means publishing (Publish) and subscription (Subscribe). In redis, you can set up message publishing and message subscription for a certain key value. When a message is published on a key 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.
2. Transactions
Who said that NoSql does not support transactions? Although redis transactions do not provide strict ACID transactions (such as a series of commands submitted for execution using EXEC, during execution If the server is down, some commands will be executed, and the rest will not be executed), but this transaction still provides the basic function of command packaging and execution (if there is no problem with the server, it can ensure that a series of commands are in order. executed together, other client commands will be inserted in the middle for execution). Redis also provides a watch function. You can watch a key and then execute the transaction. During this process, if the value of the watch is modified, the transaction will be discovered and refused to be executed.
Related recommendations: redis database tutorial
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