Embedded Java key-value storage [closed]

Question

I'm looking for a persistent key-value storage to use in my application. Specifically:

1. It must be embeddable into Java application. Pure Java solution would be the best.
2. Data must be persisted on disk, in-memory-only storage is not an option. Memory footprint size is important and overall size of key-value map can be quite large. Ideally I'd like to have some kind of LRU cache implemented over the storage.
3. Both keys & values are strings (don't need to support Java object serialization, etc).
4. Concurrent reads/writes are important.

What would be the best option in such case?

Answer 1

OrientDB (SO info page) seems to fit the bill.

The documentation is occasionally a bit lacking, but I belive it fulfills the criteria you are listing.

Answer 2

I do not know it is best or not but Hazelcast has these options. You can store your data on memory with a backup on disk. There is an example on hazelcast.