See following links
- CouchDB Vs MongoDB
- MongoDB or CouchDB – fit for production?
- DB-Engines – Comparison CouchDB vs. MongoDB
Update: I found great comparison of NoSQL databases.
MongoDB (3.2)
- Written in: C++
- Main point: JSON document store
- 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
- Has geospatial indexing and queries
- Multiple storage engines with different performance characteristics
- Performance over features
- Document validation
- Journaling
- Powerful aggregation framework
- On 32bit systems, limited to ~2.5Gb
- Text search integrated
- GridFS to store big data + metadata (not actually an FS)
- Data center aware
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.
CouchDB (1.2)
- Written in: Erlang
- Main point: DB consistency, ease of use
- License: Apache
- Protocol: HTTP/REST
- Bi-directional (!) replication,
- continuous or ad-hoc,
- with conflict detection,
- thus, master-master replication. (!)
- MVCC – write operations do not block reads
- Previous versions of documents are available
- Crash-only (reliable) design
- Needs compacting from time to time
- Views: embedded map/reduce
- Formatting views: lists & shows
- Server-side document validation possible
- Authentication possible
- Real-time updates via ‘_changes’ (!)
- Attachment handling
Best used: For accumulating, occasionally changing data, on which pre-defined queries are to be run. Places where versioning is important.
For example: CRM, CMS systems. Master-master replication is an especially interesting feature, allowing easy multi-site deployments.