This article has been arranged since childhood d Class notes and java Advanced warehouse , any similarity , Most of them are written by others

java Advanced warehouse ：https://doocs.github.io/advanced-java/#/

redis[2] redis Configuration and distributed lock introduction

Study xiao D Project notes in class

SpringDataRedis To configure RedisTemplate Introduce

• RedisTemplate Introduce
  • ValueOperations： Simple K-V operation
  • SetOperations：set Type data operation
  • ZSetOperations：zset Type data operation
  • HashOperations： in the light of map Type of data operation
  • ListOperations：list Type of data operation
• RedisTemplate and StringRedisTemplate The difference between
  • StringRedisTemplate Inherit RedisTemplate
  • The data of the two are different （ The default serialization mechanism leads to key Dissimilarity ）
  • StringRedisTemplate The default is String The serialization strategy of
  • RedisTemplate The default is JDK The serialization strategy of , The data will be sequenced into a byte array and then stored in Redis database
  • summary
    • When redis When the original operation in the database is string data , That use StringRedisTemplate that will do
    • Data is a complex object type , So use RedisTemplate It's a better choice
• operation
  • String structure
    • Store string
    • Store the object

Registration and login of case practice - Graphic verification code + Google open source Kaptcha introduce

• background
  • register - Sign in - To change the password, you usually need to send a verification code , But vulnerable to attack, malicious calls
  • What is a text message - Mailbox bomber
    • SMS bombers are a batch of 􏰀、 Loop to the mobile phone to send unlimited registration information of various websites Method of card code short message .
  • The loss of the company
    • A text message 5 Cents , If it's big 􏰀 Steal the brush and calculate by yourself Email notification is free , But it was big 􏰀 Steal brush , bandwidth 、 Connections, etc. are occupied use , It can not be used normally
• How to avoid your website becoming ” chicken “ Or be brushed
  • Add graphic captcha ( Developer )
  • single IP Limit the number of requests ( Developer )
  • Limit number sending ( Generally, SMS providers will do )
  • There is always attack and defense , It only increases the cost of attackers ,ROI Row no Naturally, I gave up
• Kaptcha The framework is introduced
  • A highly configurable practical verification of Google open source Code generation tools
    • Verification code font / size / Color
    • Scope of verification code content ( Numbers , Letter , Chinese characters !)
    • Size of captcha picture , Frame , Border thickness , Border color
    • The interference line of the verification code Style of verification code (⻥ Eye style 、3D、 Ordinary blur )

High concurrency commodity home page hot data development practice

• Hot data
  • It's often queried , But data that is not often modified or deleted
  • home page - Details page
• Link logic
  • Check whether the cache has
  • If the cache does not exist, query the database
  • Put the query results into the cache , Set expiration time
  • The next access will hit the cache
• Interface development
  • Simulating database queries takes time 200ms
  • Uncached logic ：controller-service-dao layer
  • Add cache logic ：controller-service-dao layer
• Be careful
  • Cache breakdown
  • Cache penetration
  • Cache avalanche
  • Cache and database data consistency

Jmeter5.x Pressure test tools

• LoadRunner

  • Stable performance , The results of pressure measurement and fine grain size are large , You can customize the script for pressure testing , But it's too big , There are many functions

• Apache AB( Single interface pressure measurement is the most convenient )

  • Simulate multithreaded concurrent requests ,ab Commands require very little of the computer issuing the load , It doesn't take much CPU, And it won't take up too much memory , But it can put a huge load on the target server , Simple DDOS Attack, etc

• Webbench

  • webbench First fork More than one subprocess , Each subprocess loops through web Access test . The subprocess passes the result of the visit through pipe Tell the parent process , The parent process makes the final statistics .

• Jmeter

  • Free open source , Powerful , It is widely used in Internet companies

• Local quick installation of pressure measuring tools Jmeter5.x

  • Need to install JDK8 above
  • Proposed installation JDK Environmental Science , although JRE It's fine too , But pressure measurement https need JDK Inside keytool Tools
  • Quick download https://jmeter.apache.org/download_jmeter.cgi
  • Document address ：http://jmeter.apache.org/usermanual/get-started.html

• Hot data interface pressure measurement

  • QPS: (Query Per Second): Requests per second , That is, how many requests the server processed in a second

• Add aggregation report ： Thread group -> add to -> Monitor -> Aggregation report （Aggregate Report）

 lable: sampler The name of
Samples: How many requests were sent out , for example 10 Users , loop 10 Time , It is 100
Average: Mean response time
Median: Median , That is to say 50％ User's response time
90% Line : 90％ The user's response will not exceed this time （90% of the samples took no more than this time. The remaining samples at least as long as this）
95% Line : 95％ The user's response will not exceed this time
99% Line : 99％ The user's response will not exceed this time
min : Minimum response time
max : Maximum response time
Error%： Number of wrong requests / Total number of requests
Throughput： throughput —— By default, this represents the number of requests completed per second （Request per Second) It can be compared to qps、tps
KB/Sec: The amount of data received per second

• Pressure measurement based on the current machine configuration
  • Unused cache interface
  • Use cache interface
• Problems with the current architecture

  • Distributed cache and application server network need intranet communication

  • You can deploy locally Redis To test

Introduction to the core knowledge of distributed lock and precautions

• background

  • This is to ensure that only one client can operate on shared resources at the same time

  • Case study ： The number of coupons is limited 、 The inventory of goods is oversold

  • The core

    • In order to prevent multiple processes from interfering with each other in a distributed system , We need a distributed coordination technology to schedule these processes
    • Use the mutual exclusion mechanism to control the access of shared resources , This is the problem of distributed lock

• Avoid data problems caused by concurrent operation of shared resources

  • Lock
    • Local lock ：synchronize、lock etc. , Locked in the current process , There are still problems under cluster deployment
    • Distributed lock ：redis、zookeeper Such as implementation , Although it's still locked , But lock tags shared by multiple processes , It can be used Redis、Zookeeper、Mysql And so on.

• What should be considered in designing distributed locks

  • exclusive

    • In distributed application clusters , The same method can only be executed by one thread on one machine at the same time

  • Fault tolerance

    • Distributed locks must be released , Such as client crash or network outage

  • Satisfy reentrant 、 High performance 、 High availability

  • Note the overhead of distributed locks 、 Lock granularity