Redis first meeting

1. What are the advantages and disadvantages of Redis

Advantages:

1. lIn-memory database, fast read and write speed
2. lSupport data persistence for easy backup and recovery
3. lSupports simple transactions
4. lRich data types
5. lSupport master-slave replication, sentinel mechanism

Disadvantages:

1. lData is stored in memory and is easily lost.
2. l When used as a cache, there is a problem of inconsistency with the database data
3. lavalanche problem, cache breakdown problem, cache penetration problem

Why use Redis for caching?

Cache is divided into local cache and distributed cache.Distributed caches such as redis or memcached are used. In the case of multiple instances, each instance shares a cache of data, and the cache is consistent.

Why is Redis so fast

1) Pure memory operation

Redis stores data in memory, so it is not limited by the hard disk I/O speed when reading and writing data, so it is fast

2)Single thread operation

Single thread can avoid unnecessary switching between threads and resource preemption

What is the persistence mechanism of Redis?Advantages and disadvantages of each?

1. RDB: RDB is the default persistence method of Redis.The data in the memory is saved to the hard disk in the form of snapshots according to a certain period of time.The period of the snapshot is defined by the save parameter in the configuration file.

2. AOF: Persistence is to record each write command executed by Redis to a separate log file, and restore data to the file in the Redis log when restarting.

3. When both methods are enabled at the same time, Redis will give priority to AOF recovery for data recovery.

A comparison of the two types of persistence?

• AOF files are updated more frequently than RDBs, and AOF is preferred to restore data.

• AOF is more secure and bigger than RDB

• RDB performance is better than AOF

• If both are configured with AOF first

There are usually three types of expiration policies:

• Timed Expiration: A timer needs to be created for each key whose expiration time is set, and it will be cleared immediately when the expiration time is reached.This strategy can immediately clear the expired data, which is very friendly to memory; however, it will take up a lot of CPU resources to process the expired data, thus affecting the response time and throughput of the cache.

• Lazy Expiration: Only when a key is accessed will it be judged whether the key has expired, and if it expires, it will be cleared.In extreme cases, a large number of expired keys may not be accessed again, so they will not be cleared, occupying a lot of memory.

• Regular scan: At regular intervals, the keys in the expires dictionary will be scanned, and the expired keys will be cleared.This strategy is a compromise between the first two.By adjusting the time interval of scheduled scans and the limited time-consuming of each scan, the CPU and memory resources can be optimally balanced under different circumstances.