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CouchDB is similar in many ways to MongoDB, as a document-oriented database with a JavaScript interface, but it differs in how it supports querying, scaling, and versioning. It uses a multiversion concurrency control approach, which helps with problems that require access to the state of data at various times, but it does involve more work on the client side to handle clashes on writes, and periodic garbage collection cycles have to be run to remove old data. It doesn’t have a good built-in method for horizontal scalability, but there are various external solutions like BigCouch, Lounge, and Pillow to handle splitting data and processing across a cluster of machines. You query the data by writing JavaScript MapReduce functions called views, an approach that makes it easy for the system to do the processing in a distributed way. Views offer a lot of power and flexibility, but they can be a bit overwhelming for simple queries.

Source of Information : Big data Glossary