alternative to memcached that can persist to disk

Question

I am currently using memcached with my java app, and overall it\'s working great.

The features of memcached that are most important to me are:

• it\'s fast,

Answer 1

In my experience, it is best to write an intermediate layer between the application and the backend storage. This way you can pair up memcached instances and for example sharedanced (basically same key-value store, but disk based). Most basic way to do this is, always read from memcached and fail-back to sharedanced and always write to sharedanced and memcached.

You can scale writes by sharding between multiple sharedance instances. You can scale reads N-fold by using a solution like repcached (replicated memcached).

If this is not trivial for you, you can still use sharedanced as a basic replacement for memcached. It is fast, most of the filesystem calls are eventually cached - using memcached in combination with sharedance only avoids reading from sharedanced until some data expires in memcache. A restart of the memcached servers would cause all clients to read from the sharedance instance atleast once - not really a problem, unless you have extremely high concurrency for the same keys and clients contend for the same key.

There are certain issues if you are dealing with a severely high traffic environment, one is the choice of filesystem (reiserfs performs 5-10x better than ext3 because of some internal caching of the fs tree), it does not have udp support (TCP keepalive is quite an overhead if you use sharedance only, memcached has udp thanks to the facebook team) and scaling is usually done on your aplication (by sharding data across multiple instances of sharedance servers).

If you can leverage these factors, then this might be a good solution for you. In our current setup, a single sharedanced/memcache server can scale up to about 10 million pageviews a day, but this is aplication dependant. We don't use caching for everything (like facebook), so results may vary when it comes to your aplication.

And now, a good 2 years later, Membase is a great product for this. Or Redis, if you need additional functionality like Hashes, Lists, etc.