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This article mainly introduces what is the difference between Redis and Memcache, which can be used for reference by friends who need it. I hope you will learn a lot after reading this article. Next, let the editor take you to learn about it.

Both Redis and Memcache are memory-based data storage systems. Memcached is a high-performance distributed memory caching service, which is essentially a memory key-value database. Redis is an open source key-value storage system. Similar to Memcached, Redis stores most of the data in memory, supporting data types such as strings, hash tables, linked lists, collections, ordered collections, and related operations based on these data types. So what's the difference between Memcache and Redis?

1. Different data operations

Unlike Memcached, which only supports simple key-value structure data records, Redis supports a much richer range of data types. Memcached basically only supports simple key-value storage, does not support enumeration, does not support persistence, replication and other features. Redis supports server-side data operations compared with Memcached, has more data structures and supports richer data operations, supports list, set, sorted set, hash and many other data structures, but also provides persistence and replication and other functions.

Usually in Memcached, users need to take the data to the client to make similar modifications and then set back, which greatly increases the number of network IO and data volume. In Redis, these complex operations are usually as efficient as normal GET/SET. So, if you need caching to support more complex structures and operations, Redis would be a better choice.

2. Different memory management mechanisms

In Redis, not all data is stored in memory all the time. This is the biggest difference compared with Memcached. When physical memory is used up, Redis can swap some value that has not been used for a long time to disk. Redis only caches all key information. If Redis finds that the memory usage exceeds a certain threshold, it triggers the operation of swap, and Redis calculates which value corresponding to key needs to be swap to disk based on "swappability = age*log (size_in_memory)". The value corresponding to these key is then persisted to disk and cleared in memory. This feature allows Redis to maintain more data than the memory of its machine itself.

Memcached uses Slab Allocation mechanism to manage memory by default, and its main idea is to divide the allocated memory into blocks of specific length to store key-value data records of corresponding length according to the predetermined size, so as to completely solve the problem of memory fragmentation.

In terms of memory utilization, using simple key-value storage, Memcached has a higher memory utilization. If Redis uses hash structure to do key-value storage, because of its combined compression, its memory utilization will be higher than Memcached.

3. Different performance

Because Redis uses only a single core, while Memcached can use multiple cores, on average, Redis performs better than Memcached in storing small data on each core. In the data of more than 100k, the performance of Memcached is higher than that of Redis. Although Redis has also optimized the performance of storing big data, it is still slightly inferior to Memcached.

4. Different cluster management

Memcached is a full memory data buffer system. Although Redis supports data persistence, full memory is the essence of its high performance after all. As a memory-based storage system, the size of machine physical memory is the maximum amount of data that the system can hold. If the amount of data that needs to be processed exceeds the physical memory size of a single machine, you need to build a distributed cluster to expand storage capacity.

Memcached itself does not support distributed storage, so distributed storage of Memcached can only be realized on the client side through distributed algorithms such as consistent hashing. Compared with Memcached, which can only implement distributed storage on the client side, Redis prefers to build distributed storage on the server side.

Thank you for reading this article carefully. I hope it will be helpful for everyone to share the difference between Redis and Memcache. At the same time, I also hope you will support us, pay attention to the industry information channel, and find out if you encounter problems. Detailed solutions are waiting for you to learn!

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