Memcached真的过期了吗？

这两年Redis火得能够，Redis也经常被看成Memcached的挑战者被提到桌面上来。关于Redis与Memcached的比较更是比比皆是。然而，Redis真的在功能、性能以及内存使用效率上都超越了Memcached吗？

下面内容来自Redis做者在stackoverflow上的一个回答，对应的问题是《Is memcached a dinosaur in comparison to Redis?》（相比Redis，Memcached真的过期了吗？）

• You should not care too much about performances. Redis is faster per core with small values, but memcached is able to use multiple cores with a single executable and TCP port without help from the client. Also memcached is faster with big values in the order of 100k. Redis recently improved a lot about big values (unstable branch) but still memcached is faster in this use case. The point here is: nor one or the other will likely going to be your bottleneck for the query-per-second they can deliver.

• 没有必要过多的关心性能，由于两者的性能都已经足够高了。因为Redis只使用单核，而Memcached能够使用多核，因此在比较上，平均每一 个核上Redis在存储小数据时比Memcached性能更高。而在100k以上的数据中，Memcached性能要高于Redis，虽然Redis最近 也在存储大数据的性能上进行优化，可是比起Memcached，仍是稍有逊色。说了这么多，结论是，不管你使用哪个，每秒处理请求的次数都不会成为瓶 颈。（好比瓶颈可能会在网卡）

• You should care about memory usage. For simple key-value pairs memcached is more memory efficient. If you use Redis hashes, Redis is more memory efficient. Depends on the use case.

• 若是要说内存使用效率，使用简单的key-value存储的话，Memcached的内存利用率更高，而若是Redis采用hash结构来作key-value存储，因为其组合式的压缩，其内存利用率会高于Memcached。固然，这和你的应用场景和数据特性有关。

• You should care about persistence and replication, two features only available in Redis. Even if your goal is to build a cache it helps that after an upgrade or a reboot your data are still there.

• 若是你对数据持久化和数据同步有所要求，那么推荐你选择Redis，由于这两个特性Memcached都不具有。即便你只是但愿在升级或者重启系统后缓存数据不会丢失，选择Redis也是明智的。

• You should care about the kind of operations you need. In Redis there are a lot of complex operations, even just considering the caching use case, you often can do a lot more in a single operation, without requiring data to be processed client side (a lot of I/O is sometimes needed). This operations are often as fast as plain GET and SET. So if you don’t need just GEt/SET but more complex things Redis can help a lot (think at timeline caching).

• 固然，最后还得说到你的具体应用需求。Redis相比Memcached来讲，拥有更多的数据结构和并支持更丰富的数据操做，一般在 Memcached里，你须要将数据拿到客户端来进行相似的修改再set回去。这大大增长了网络IO的次数和数据体积。在Redis中，这些复杂的操做通 常和通常的GET/SET同样高效。因此，若是你须要缓存可以支持更复杂的结构和操做，那么Redis会是不错的选择

来源：Is memcached a dinosaur in comparison to Redis?（其余人的回答一样值得一看）