Redis persistence, memory configuration and cache issues

Xiaofei 2020-11-09 22:19:08
redis persistence memory configuration cache


About Redis Configuration instructions

Redis Description of persistence

redis Data persistence is supported by default , When redis When there is data in, the data will be saved to disk regularly , When redis When the server restarts, it will read the specified persistent file according to the configuration file , Realize the recovery of memory data .

Persistence mode

RDB Pattern

characteristic :
1.RDB The pattern is redis The default persistence policy for .
2.RDB The pattern records redis Snapshot of memory data , The latest snapshot will cover the previous content , all RDB Persistent files take up less space , Persistence is more efficient .
3.RDB Patterns are persisted on a regular basis , So it may lead to the loss of data .

command :

  1. save Requires immediate and immediate persistence Synchronous operation Other redis The operation will get stuck .
  2. bgsave Turn on background operation Asynchronous operations Because of asynchronous operation , So there's no guarantee rdb The files must be up to date and need to wait .

To configure :
1. Persistent file name
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2. Persistent file location
dir./ The relative path .
dir/usr/local/src/redis How to write absolute path .
image.png
3.RDB Pattern persistence strategy
image.png

AOF Pattern

characteristic :
1.AOF Mode is off by default , Manual opening required .
image.png
2.AOF Patterns are asynchronous operations , It records the process of user's operation , It can prevent users from losing data .
3. because AOF Patterns record the running state of a program , So the persistence file is relatively large , It takes a long time to recover data , Need to optimize persistence files artificially .
To configure :
image.png
summary :
1. If data loss is not allowed , Use AOF Pattern .
2. If we pursue efficiency , Allow a small amount of data loss , use RDB Pattern .
3. If the minutes guarantee efficiency , And to ensure the data , You should configure redis The cluster of , Host use RDB Pattern , The slave machine uses AOF Pattern .

About Redis Memory strategy

An explanation of the memory policy

Redis Data is stored in memory . If you keep storing data in memory It will inevitably lead to the overflow of memory data .
Solution :

  1. Keep as much as possible in redis Data addition timeout in .
  2. Using algorithms to optimize old data .

LRU Algorithm

characteristic : The best memory optimization algorithm to use .
LRU yes Least Recently Used Abbreviation , namely Recently at least use , Is a commonly used data replacement algorithm , Choose the most recently unused data for elimination . The algorithm gives each data an access field , It is used to record the time that a data has experienced since it was last accessed t, When a data has to be eliminated , Select the existing data t The most valuable , That is, the least recently used data will be eliminated .
dimension : Time T

LFU Algorithm

LFU(least frequently used (LFU) page-replacement algorithm). That is, the least frequent use of page replacement algorithm , It is required to replace the page with the lowest reference count at page replacement , Because frequently used pages should have a large number of references . But some pages are used a lot at the beginning , But it will not be used in the future , Such pages will stay in memory for a long time , So we can introduce Use the count register to shift right one bit at a time , The average number of uses to form an exponential decay .
dimension : Times of use

RANDOM Algorithm

That is to delete data randomly .

TTL Algorithm

The algorithm to delete the data with time-out in advance .

Redis Memory data optimization

1.volatile-lru The data with time-out is used lru Algorithm .
2.allkeys-lru All the data use LRU Algorithm .
3.volatile-lfu The data with time-out is used lfu Algorithm delete .
4.allkeys-lfu All the data are based on lfu Algorithm delete .
5.volatile-random The data of setting time-out time adopts random algorithm .
6.allkeys-random Random algorithms for all data .
7.volatile-ttl Set the timeout data TTL Algorithm .
8.noeviction If memory overflows It will report an error and return . Do nothing . The default value is .
image.png

About Redis The cache problem

Problem description : If massive users request at the same time And then redis Server problem It may cause the whole system to crash .
Running speed :

  1. tomcat The server 150-250 Between JVM tuning 1000/ second
  2. NGINX 3-5 ten thousand / second
  3. REDIS read 11.2 ten thousand / second Write 8.6 ten thousand / second Average 10 ten thousand / second

Cache penetration

Problem description : Because of users High concurrency Visit in the environment Data that does not exist in the database , Easy to cause cache penetration .
Solution : Set up IP Current limiting operation nginx in Or Microsoft Service Mechanism API Gateway implementation .

Cache breakdown

Problem description : Because of users High concurrency In the environment , Because some data existed in memory before , But for special reasons ( Data timeout / Data accidentally deleted ) Lead to redis Cache invalidation . So that a large number of users' requests directly access the database .
Solution :
1. When setting the timeout Don't set the same time .
2. Set multi level cache .
image.png

Cache avalanche

Problem description : because High concurrency Under the condition of Yes A lot of data failed . Lead to redis The hit rate is too low . It allows users to access the database directly ( The server ) Cause crash , It's called cache avalanche .
Solution :
1. Don't set the same timeout random number
2. Set multi level cache .
3. Improve redis Cache hit rate adjustment redis Memory optimization strategy use LRU And so on .
image.png

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