Why Graylog2 uses MongoDB:
So we need something in between: schema-less storage with indexes, everything else are bonuses. With Mongo DB we got a lot of them:
- capped collections, which preserve insertion order and maximum collection size, automatically removing old messages;
- tailed cursors, which are used to implement tail -f behavior;
- awesome performance;
- and an easy API.
Original title and link: Graylog2: MongoDB for Centralizing Logging (NoSQL databases © myNoSQL)