Cassandra – “Cassandra is a highly scalable, eventually consistent, distributed, structured key-value store. Cassandra brings together the distributed systems technologies from Dynamo and the data model from Google’s BigTable. Like Dynamo, Cassandra is eventually consistent. Like BigTable, Cassandra provides a ColumnFamily-based data model richer than typical key/value systems.”

The huge appeal of Cassandra seems to be the approach to make it highly fault-tolerant. Writes never fail. Data is always available. No single point of failure. If you’re making a Twitter-like app, you should consider it.

Tokyo Cabinet – “Tokyo Cabinet uses hash algorithm to retrieve records. If a bucket array has sufficient number of elements, the time complexity of retrieval is “O(1)”. That is, time required for retrieving a record is constant, regardless of the scale of a database. It is also the same about storing and deleting. Collision of hash values is managed by separate chaining. Data structure of the chains is binary search tree. Even if a bucket array has unusually scarce elements, the time complexity of retrieval is “O(log n)”.”

Tokyo Cabinet is slightly newer and is apparently stupidly fast, faster than any other storage solutions out there (at least for now). It’s written in C and provided as API of C, Perl, Ruby, Java, and Lua.

Do you know anyone who has used these two already? Care to share your experiences?