> How would doing something like this with CouchDB and Lounge compare > with using Hadoop and HBase?
Remember that CouchDB and Hadoop serve different purposes. CouchDB is a data store, where as Hadoop is a data processing platform. While they both have "MapReduce" functionality they aren't quite the same thing. In CouchDB, when we use Map/Reduce, we create a single persistent index of data using map and reduce operators. These indexes can then be queried using single key or range lookups. Because of the properties of Map/Reduce we're capable of updating these indexes incrementally. Hadoop on the other hand is meant to handle arbitrary pipelines of data processing. Ie, users can configure Hadoop to run multiple stages of Map/Reduce in order to produce some desired output. The intermediate stages are not intended to be persistent and query-able. I'm not familiar enough to know how people use HBase in conjunction with Hadoop other than I believe its generally a data source. I don't know if it stores intermediate results or not. As far as I know, Hadoop doesn't provide incremental indexing. As Randal points out, there are various differences in implementation, but its also important to understand the data store vs. data processing differences of the two systems. HTH, Paul Davis
