Redis introduction

One 、Redis Introduce

  Redis It's based on key value pairs （key-value） In-memory database , among value It can be for string、hash、list、set、zset And other data structures , It can satisfy many application scenarios . Key expiration is also provided 、 Publish subscribe 、 Business 、 Pipeline and other additional functions .

   characteristic
  1) Fast
   Official read / write performance 10 ten thousand /s（ It's about machine performance ）.

 The main reason for the speed ：
a)	 Data is stored in memory 
b)	C Language implementation , Close to the operating system 
c)	 A single threaded architecture is used , Prevent possible contention problems caused by multithreading 

  2) Data structure of key value pair

  3) Rich functions

  4) Simple and stable , Single thread

  5) Persistence
   Data persistence to hard disk

  6) Master slave copy
   Realize multiple copies of the same data

  7) Highly available and distributed
   Sentinel mechanism to achieve high availability , Guarantee redis Node fault detection and automatic transfer .

  8) The client supports multiple languages
   Support java、php、python、c、c++、nodejs etc. .

   Use scenarios
  1) Cache database
  2) Distributed lock
  3) Publish subscribe
  4) Ranking List
  5) Counter application
  6) Social networks
  7) Current limiting
  

Two 、Redis data structure

2.1 character string （String）

   It can actually be a string （ Include XML JSON）、 Numbers 、 Base number （ picture Audio video ）, Maximum not exceeding 512MB.

   Set value command

SET key value [EX seconds]
MSET key value [key value ...]

   Value command

GET key
MGET key [key ...]

   Count command

INCR key                     // Integral plus 1, Non integer return error .key Create if it does not exist , And back to 1.
DECR key;                    // reduce 1
INCRBY key increment         // Increase the given value 
DECRBY key increment         // Subtract the given value 
INCRBYFLOAT key increment    // Increase the given floating-point value 

   Other commands

APPEND key value         // Append string 
STRLEN key               // Get string length 
GETRANGE key start end   // Intercepting string 

  

2.2 Hash （hash）

  hash It's a string Type of field and value Mapping table , Suitable for storing objects .

   Common command

HSET key field value [field value ...]
HMSET key field value [field value ...]
HGET key field
HMGET key field [field ...] 

HDEL key field [field ...]
HLEN key 						// return field The number of 
HEXISTS key field 				// Judge field Whether there is 
HKEYS key 						// Get all field
HVALS key 						// Get all value
HGETALL key 					// Get all field and value
HINCRBY key field increment
HINCRBYFLOAT key field increment

  

2.3 list （list）

   Used to store multiple ordered strings , A list can save up to 232 - 1 Elements .

   Add command

RPUSH key element [element ...]          // Add from right 
LPUSH key element [element ...]          // Add... From the left 
LINSERT key BEFORE|AFTER pivot element   // Insert before or after the specified element .

   Search for commands

LRANGE key start stop
LINDEX key index 		// Get elements by subscript 

   The delete command

LPOP key [count] // Delete the specified number of elements from the left 
RPOP key [count] // Delete the specified number of elements from the right 
LREM key count element // remove count Specified elements ,count>0 Remove from left to right ;count<0 Remove from right to left ,count=0  Remove all .
LTRIM key start stop // Delete elements outside the specified range 

   Modify the order

LSET key index element // Modify the specified subscript element 

   Other commands

LLEN key // Get list size 

  

2.4 aggregate （set）

   Add command

SADD key member [member ...]

   Search for commands

SMEMBERS key // Return all elements 
SRANDMEMBER key [count] // Random return count Elements 
SCARD key // Returns the number of collection elements 

   The delete command

SREM key member [member ...] 	// Remove elements 
SPOP key [count] 				// Randomly delete and return count Elements 

   Other commands

SISMEMBER key member 			// Determine whether there are elements in the set 
SINTER key [key ...] 			// Returns the intersection of sets 
SUNION key [key ...] 			// Returns the union of sets 
SDIFF key [key ...] 			// Returns the difference set of a set 

2.5 Ordered set （zset）

ZADD key score member [score member ...]	// Add or modify 
ZRANGE key min max [WITHSCORES] 			// Check out the elements 
ZREVRANGE key min max [WITHSCORES] 			// Check out the elements 
ZSCORE key member							// View element scores 

ZINCRBY key increment member 				// Elements increase scores 

ZCARD key 									// Count the number of elements 
ZCOUNT key min max 							// Returns the number of elements within the specified score range 

ZREM key member [member ...] 				// Remove elements 
ZREMRANGEBYSCORE key min max 				// Delete elements in the specified score range 

ZRANK key member 							// Returns the subscript of the element in positive order according to the fraction 
ZREVRANK key member 						// Returns the subscript of the element flashback according to the score 

ZRANGEBYSCORE key min max [WITHSCORES] 		// Returns the elements within the specified score range , positive sequence 
ZREVRANGEBYSCORE key min max [WITHSCORES]   // Returns the elements within the specified score range , In reverse order 

ZINTERSTORE destination numkeys key [key ...] [WEIGHTS weight] [AGGREGATE SUM|MIN|MAX] // Find the intersection 

  

3、 ... and 、 Redis Persistence

  Redis Is a memory database that supports persistence , Persistence can avoid data loss caused by process exit . There are ways to persist RDB、AOF Two kinds of .

  RDB（Redis DataBase）
   It refers to writing the data set snapshot in memory to disk within a specified time interval . It's also the default way to persist .
  RDB The trigger methods are ：
  1) save command
    This command will block the current Redis, perform save During the order ,Redis Can't handle other orders . If the memory instance is more likely to cause long-term blocking , It is not recommended for online environment .
  2) bgsave command
    Redis Process execution Action create subprocess , Persistence is done by child processes . The blockage only happens in fork Stage , Time is very short （ Subtlety ）. Basically Redis Internally owned RDB The operation is to use bgsave command .
  3) Automatic triggering
    Automatically trigger according to the configuration file .

   advantage ：
  1) Compressed binary text , For backup 、 Copy in full , For disaster recovery .
  2) load RDB Recover data much faster than AOF The way .

   shortcoming ：
  1) Unable to achieve real-time persistence , Create subprocesses every time , Frequent operation cost is too high .
  2) Saved binary , The old version is not compatible with the new version rdb Problems with documents .
  3) Since the child process is started for persistence , There may be a small amount of data loss .

  AOF（Append Only File）
  Redis Will pass every written order received write Function appended to file . The common sense is to log .

  AOF technological process ：

  1) All write commands (set hset) Will add （append） To aof_buf Buffer zone .
  2) AOF The buffer synchronizes with the hard disk （sync）
  3) With AOF The files are getting bigger , Need to check AOF File rewriting （rewrite）, Compression reached .
  4) When redis Service to restart , can load load AOF File for recovery .

  AOF Trigger mode ：
  1)always
     Synchronous operation , Every time there is a data change, it will be recorded to the disk immediately , Poor performance but good data integrity .
  2)everysec
     Asynchronous operations , Record every second If it goes down in a second , There is data loss
  3)no
     Fully dependent on the operating system , Best performance , Persistence cannot be guaranteed （ Synchronization of the operating system itself ）.

   advantage ：
  1) AOF Better protect data from loss .
  2) AOF The log file does not have any disk addressing overhead , Very high write performance , Documents are not easy to break .
  3) AOF Even when the log file is too large , Background override operation occurred , It will not affect the client's reading and writing .

   shortcoming ：
  1) For the same data ,AOF Log files are usually larger than RDB Larger data snapshot file .
  2) AOF After opening , Supporting writing QPS than RDB Supporting writing QPS low .
  

Four 、Redis Publish subscribe

  Redis Publish subscribe (pub/sub) It's a message communication mode ： sender (pub) Send a message , subscriber (sub) receive messages .Redis Clients can subscribe to any number of channels .

   first redis-cli client

redis 127.0.0.1:6379> SUBSCRIBE chat

Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "runoobChat"
3) (integer) 1

   the second redis-cli client

redis 127.0.0.1:6379> PUBLISH chat"Redis PUBLISH test"

(integer) 1

redis 127.0.0.1:6379> PUBLISH chat"Learn redis by runoob.com"

(integer) 1

#  The subscriber's client will display the following message 
 1) "message"
 2) "chat"
 3) "Redis PUBLISH test"
 1) "message"
 2) "chat"
 3) "Learn redis by runoob.com"

  

5、 ... and 、Redis Business

   In depth understanding of Redis Business
  

6、 ... and 、Redis Distributed lock

   Distributed lock implementation principle