Redis overview

One 、 summary

• Redis Full name Remote Dictionary Server, Remote dictionary service , Is an open source use ANSI C Language writing 、 Support network 、 Log type that can be memory based or persistent 、Key-Value database , And provide multilingual API.

Two 、 Definition

• Redis It's a key-value The storage system . and Memcached similar , It supports storage value There are more types , Include string( character string )、list( Linked list )、set( aggregate )、zset(sorted set -- Ordered set ) and hash（ Hash type ）. These data types support push/pop、add/remove And take intersection, union and difference sets and more abundant operations , And these operations are atomic . On this basis ,redis Support various sorts of sorting . And memcached equally , To ensure efficiency , The data is cached in memory . The difference is redis Periodically, updated data is written to disk or changes are written to an appended log file , And on this basis to achieve master-slave( Master-slave ) Sync .
• Redis Is a high-performance key-value database . Redis Appearance , A lot of compensation memcached This kind of key/value Insufficient storage , In the department The situation can be a good complement to the relational database . It provides Java,C/C++,C#,PHP,JavaScript,Perl,Object-C,Python,Ruby,Erlang Such as the client , Easy to use .  
• Redis Support master-slave synchronization . Data can be synchronized from the master server to any number of slaves , A slave server can be the master server associated with other slaves . This makes Redis Single-layer tree replication can be performed . The disk can write to the data intentionally or unintentionally . Due to the full implementation of the release / Subscribe mechanism , Enables trees to be synchronized anywhere from the database , Subscribe to a channel and receive a complete record of message publication from the master server . Synchronization helps with scalability and data redundancy for read operations .
• Redis Official website ：redis.io.（ The domain name suffix io It's a country domain , yes british Indian Ocean territory, The British Indian Ocean territory ）,Vmware In the fund redis Project development and maintenance .

3、 ... and 、 Data model

• Redis The periphery of the is made up of a key 、 Dictionary composition of value mapping . The main difference from other non relational databases is ：Redis The type of median is not limited to strings , The following abstract data types are also supported ：
  • String list
  • An unordered collection of unrepeated strings
  • An ordered set of non repeating strings
  • key 、 Hash table with string values
• The type of value determines the operation that the value itself supports .Redis Support different kinds of disorder 、 An orderly list , disorder 、 The intersection of ordered sets 、 Union and other advanced server-side atomic operations .

Four 、 data structure

Redis There are five types of data ：string,hash,list,set And zset(sorted set).

• string（ character string ） Is the simplest type , You can understand that Memcached As like as two peas , One key Corresponding to one value, Supported operations and Memcached Similar to . But it's more functional .Redis Using structure sdshdr and sds Encapsulates the string , String related operations are implemented in the source file sds.h/sds.c in .
• list( Double linked list ) Is a linked list structure , The main functions are push、pop、 Get all the values of a range and so on . In operation key The name of the list . Yes list The definition and implementation of is in the source file adlist.h/adlist.c
• dict(hash surface ) set Is a collection , Similar to the concept of set in our mathematics , Operations on collections include adding and deleting elements , There are operations such as intersection and difference of multiple sets . In operation key The name of a collection . In the source file dict.h/dict.c Implemented in the hashtable The operation of .dict in table by dictEntry An array of pointers , Each member in the array is hash One way linked list of elements with the same value .set Is in dict On the basis of implementation , It specifies key The comparison function of is dictEncObjKeyCompare, if key If it is equal, it will not be inserted .
• zset( Sort set) yes set An updated version of , He was in set Add a sequence attribute based on the , This attribute can be specified when adding modification elements , After each assignment ,zset Automatically reorder to the new value . Understandably, there are two columns of mysql surface , List store value, One column storage order . In operation key Understood as a zset Name .zset utilize dict maintain key -> value The mapping relation of , use zsl(zskiplist) preservation value Ordered relation of .zsl It's actually a cross . Unstable multitree , The elements on each chain are sorted in ascending order from the root node to the leaf node .

5、 ... and 、 Store

Redis Two file formats are used ： Full data and incremental requests .

• Full data format is to write data in memory to disk , It is convenient to read the file for loading next time ;
• Incremental request file is to serialize the data in memory into operation request , Used to read files for replay Get data , Serialization operations include SET、RPUSH、SADD、ZADD.

Redis The storage of is divided into memory storage 、 Disk storage and log Three parts of the document , There are three parameters in the configuration file to configure it .

• save seconds updates,save To configure , Indicate how long , How many update operations are there , Synchronize the data to the data file . This can be combined with multiple conditions , Such as the Settings in the default configuration file , There are three conditions .
• appendonly yes/no ,appendonly To configure , Indicates whether to log after each update operation , If you don't turn it on , Data may be lost for a period of time during a power outage . because redis To synchronize the data file itself, press the above save Condition to synchronize , So some data will only exist in memory for a while .
• appendfsync no/always/everysec ,appendfsync To configure ,no Means that the operating system synchronizes the data cache to disk ,always Represents a manual call after each update operation fsync() Write data to disk ,everysec That means once per second .

6、 ... and 、 install And To configure

• Windows Next Redis install ：win10 Install redis_JAVA·Ｄ·WangJing The blog of -CSDN Blog _redis win10 Installation package
• Linux Next Reids install ：Linux Next Redis Installation and configuration （yum Software source download and installation ）_JAVA·Ｄ·WangJing The blog of -CSDN Blog _redis yum Source
• Docker Next Redis install ：Docker Next Redis install _JAVA·Ｄ·WangJing The blog of -CSDN Blog
• Redis Service configuration redis.conf Configuration file details ：Redis Service configuration redis.conf Configuration file details _JAVA·Ｄ·WangJing The blog of -CSDN Blog _redisconf Storage location
• Redis Ban Dangerous orders ：Redis Ban Dangerous orders _JAVA·Ｄ·WangJing The blog of -CSDN Blog _redis To disable the command

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