Kristof Kovacs put together an excellent comparisons of the different NoSQL products. Here are the products it covers.

• MongoDB
• Riak
• CouchDB
• Redis
• HBase
• Neo4j
• Cassandra
• Membase

Cassandra vs MongoDB vs CouchDB vs Redis vs Riak vs HBase vs Membase vs Neo4j comparison

By Kristof Kovacs

While SQL databases are insanely useful tools, their monopoly of ~15 years is coming to an end. And it was just time: I can't even count the things that were forced into relational databases, but never really fitted them.

But the differences between NoSQL databases are much bigger than it ever was between one SQL database and another. This means that it is a bigger responsibility on software architects to choose the appropriate one for a project right at the beginning.

In this light, here is a comparison of Cassandra, Mongodb, CouchDB, Redis, Riak, Membase, Neo4j andHBase:

1. MongoDB

• Written in: C++
• Main point: Retains some friendly properties of SQL. (Query, index)
• License: AGPL (Drivers: Apache)
• Protocol: Custom, binary (BSON)
• Master/slave replication (auto failover with replica sets)
• Sharding built-in •Queries are javascript expressions
• Run arbitrary javascript functions server-side
• Better update-in-place than CouchDB
• Uses memory mapped files for data storage
• Performance over features
• Journaling (with --journal) is best turned on
• On 32bit systems, limited to ~2.5Gb
• An empty database takes up 192Mb
• GridFS to store big data + metadata (not actually an FS)
• Has geospatial indexing

Best used: If you need dynamic queries. If you prefer to define indexes, not map/reduce functions. If you need good performance on a big DB. If you wanted CouchDB, but your data changes too much, filling up disks.

For example: For most things that you would do with MySQL or PostgreSQL, but having predefined columns really holds you back.

Read full article at http://kkovacs.eu/cassandra-vs-mongodb-vs-couchdb-vs-redis