Basic introduction of redis and explanation of eight types and transactions

Redis

Redis It's single threaded

Redis It's very fast , The official website said ,Redis It's based on memory operations ,CPU No Redis Performance bottleneck ,Redis The bottleneck is based on the memory and network bandwidth of the machine , Now that you can use a single path to implement , Single thread is used .

Redis yes C Written language , The official data is 100000+ Of QPS, It's not the same as using key-value Of Memecache Bad

Redis Why is single thread so fast ?

• boring 1: High performance servers are not necessarily multithreaded

• myth 2: Multithreading (CPU The context switches !), It must be more efficient than a single thread !

Go first CPU> Memory > To understand the speed of the hard disk

The core :redis Is to put all the data in memory , So using single thread to operate is the highest efficiency , Multithreading (CPU Will switch context : Time consuming operations ), For memory systems , If there is no context switch , Efficiency is the highest . Read and write many times in the same CPU Upper , In the case of memory , This is the best solution .

Redis Eight storage types

String

APPEND haha f
get haha# The value is f

List

• list , Queues and stacks can be implemented

LPUSH list one# Stack insert 
LPUSH list two
LPUSH list three
LRANGE list 0 -1# Get all by default list====>three,two,one
LRANGE list 0 1# obtain 0 and 1 The elements of ,three two
RPUSH list haha# Queue insertion 
LRANGE list 0 -1# Get all by default list====>three,two,one,haha

Set

• It's simple , Check on the official website

Hash

• It's simple , Check on the official website

Zset

• Ordered set , Can sort

  • Rank salary

Geospatial

• Map

  • Enter the city name , Latitude and longitude , Then you can calculate the distance or people nearby

Hyperloglog

• Radix sorting

PFadd mykey a b c d e f g h i j# Create the first set of elements mykey
PFCOUNT mykey# obtain 10
PFadd mykey2 i j z x c v b n m
PFCOUNT mykey2# obtain 9
PFMERGE mykey3 mykey mykey2# Combine 
PFCOUNT mykey3# obtain 15

• Web page UV( A person visits many times , Finally, it's one more time )

Bitmap

• Bitmap (0 and 1 The status code )

setbit haha 0 1
setbit haha 1 1
setbit haha 2 0
getbit haha 2# obtain 0
bitcount haha 0 2# from key0 To key2 Get value 1
bitcount haha# Get all values by default 1

• Log in , Is it active , Whether to punch in or not

• It can be used bigcount Calculate how much 0 and 1

Redis The business of

Mybatis Transactions in have four characteristics ,ACID: Atomicity , Uniformity , Isolation, , persistence

but Redis A single command saves atomic , But transactions don't guarantee atomicity

multi#OK, Open transaction 
set k1 v1# Set up 
set k2 v2# Set up 
get k2# Get no value , Only return QUEUE
set k3 v3
exec# perform , Then the return value of the previous command appears , as follows 
#1) OK
#2) OK
#3) "v2"
#4) OK
# After each execution, you need to write it again multi

Redis Transaction exception

Compiler exception ( Something is wrong with the code ! There was a mistake in the order !), All commands in the transaction will not be executed !

multi#OK
set k1 v1
getset k2#(error) ERR wrong number of arguments for 'getset' command
set k3 v3
exec#(error) EXECABORT Transaction discarded because of previous errors.
get k2#(nil), empty , Don't do anything 

Runtime exception (1/0 One divided by 0), If there are similar exceptions in the transaction queue , So when you execute an order , Other commands can be executed normally , An error command throws an exception

set k1 v1
multi
incr k1# There is no abnormality for the time being , Because the grammar is right 
set k2 v2
set k3 v3
get k3
exec# After execution , It can still be executed , It's just incr k1 The statement doesn't work 
#1) (error) ERR value is not an integer or out of range
#2) OK
#3) OK
#4) "v3"

Redis Monitoring test ( Optimism lock )

Normal execution succeeded !

set money 100
set out 0
WATCH money# monitor money
MULTI
DECRBY money 20
INCRBY out 20
exec# success , Because there is no other thread interference , as follows , Transfer succeeded 
#80
#20

Normal execution is unsuccessful !( Testing multithreaded modification values , Use watch Can be regarded as redis Optimistic lock operation of )

WATCH money
MULTI# Business 
DECRBY money 10
INCRBY out 10
exec# Before entering this command , Other thread pairs money It's been modified , Then we entered exec, Then the execution error is displayed 
UNWATCH# Unlock