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In this article, the editor introduces "when to choose Redis" in detail, the content is detailed, the steps are clear, and the details are handled properly. I hope this "when to choose Redis" article can help you solve your doubts.

1. Complex data structure, redis is more appropriate.

When value is a complex data structure such as hash, list, collection, and ordered collection, redis is chosen because mc cannot meet these requirements.

The most typical scenario, user order list, user message, post comment list, etc.

Second, persistence is more appropriate to choose redis.

Mc cannot meet the need for persistence, so it has to choose redis. But here's a reminder: are you really using redis's persistence feature correctly?

Never use redis as a database:

Regular snapshots of redis cannot guarantee that data will not be lost

Redis's AOF reduces efficiency and cannot support too much data.

Do not expect redis to do better than mysql for solidified storage. Different tools do what they are good at and use redis as a database. This design is probably wrong.

What are the advantages and disadvantages of caching the scene and turning on the solidification function?

If it is only a cache scenario, and the data is stored in the database and cached in redis, if the solidification feature is enabled:

The advantage is that when redis is hung up and then restarted, hot data can be recovered quickly in memory, without instantaneous pressure on the database, and there is no cache preheating process.

The disadvantage is that in the process of redis hanging, if there are changes to the data in the database, it may cause the data of the database to be inconsistent with that of redis after redis restart.

Therefore, read-only scenarios, or allow some inconsistent business scenarios, can try to turn on the solidification of redis.

3. High availability, redis is more appropriate

Redis naturally supports clustering function, which can achieve active replication and read-write separation.

Redis officially also provides sentinel cluster management tools, which can achieve master-slave service monitoring and automatic failover, all of which are transparent to the client without program changes or human intervention.

Voiceover: memcache, to achieve high availability, you need to carry out secondary development, such as double reading and writing on the client side, or cluster synchronization on the server side.

However, I would like to remind you that in most business scenarios, does caching really need to be highly available?

Caching scenarios, in many cases, allows cache miss

The cache is dead, and data can be read through DB in many cases.

So, you need to carefully analyze the business scenario, high availability, is it really the main requirement for caching?

Voiceover: in the instant messaging business, the online status of users has a high demand for availability.

Fourth, the content of storage is relatively large, so it is more appropriate to choose redis

The maximum value storage for memcache is 1m. If the value stored is very large, only redis can be used.

Of course, compared with memcache, redis also has some "disadvantages" due to the differences in the underlying implementation mechanism.

Case 1: due to differences in memory allocation mechanisms, redis may cause memory fragmentation

Memcache manages memory by pre-allocating memory pools, saving memory allocation time.

Redis is a temporary application for space, which may lead to debris.

At this point, mc will be faster.

Case 2: due to differences in virtual memory usage, redis may affect performance by brushing the disk.

Memcache stores all the data in physical memory.

Redis has its own VM mechanism, which can theoretically store more data than physical memory. When the data exceeds, it will trigger swap and brush the cold data onto the disk. At this point, mc is faster when there is a large amount of data.

Voice-over: the new version of redis has been optimized.

Case 3: due to differences in network models, redis may affect IO scheduling because of CPU computing

Memcache uses the non-blocking IO reuse model, and redis also uses the non-blocking IO reuse model.

However, because redis also provides some sorting and aggregation functions outside of non-KV storage, complex CPU calculations block the entire IO scheduling when performing these functions.

At this point, because redis provides more features, mc will be faster.

Case 4: due to differences in threading models, it is difficult for redis to use multicore special effects to improve performance

Memcache uses multithreading, the main thread listens, and the worker child thread accepts requests and performs reads and writings. During this process, there may be lock conflicts.

Redis uses single thread, although there are no lock conflicts, but it is difficult to take advantage of the multi-core feature to improve the overall throughput.

At this point, mc will be faster.

Case 5: due to the lack of auto-sharding,redis, we can only scale horizontally manually.

Whether it is redis or memcache, the server cluster does not naturally support horizontal expansion and needs to be shredded on the client, which is actually not friendly to the caller. If the server cluster can support horizontal expansion, it will be more perfect.

Finally, it may be one of the reasons why many people like redis: the source code is highly readable and the code is of high quality.

After looking at the source code of redis and memcache, in terms of readability, redis is the cleanest software I have ever seen, not even one of them, or even one of the original intentions of redis design. Compiling redis does not even require configure, and does not need to rely on third-party libraries. A make is done.

And the memcache source code, may be considering too much expansibility, multi-system compatibility, the code is not clean, looks laborious.

For example, in the part of the network IO, 1-2 files of redis source code are done. Mc uses libevent, a fd is passed over, and pipe is passed on by threads, which is particularly easy to make people dizzy.

After reading this, the article "when to choose Redis" has been introduced. If you want to master the knowledge points of this article, you still need to practice and use it yourself to understand it. If you want to know more about related articles, welcome to follow the industry information channel.

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