What is the use of MongoDB in GrayLog2?

Question

GrayLog2 requires both ElasticSearch and MongoDB, while Logstash uses only ElasticSearch for persisting and searching the logs. what does mongo provide in graylog2?

Answer 1

Graylog2 uses mongodb for the web interface entities. Streams, alerts, users, settings, cached stream counts etc. Pretty much everything you see and edit in the web interface except for the logs themselves.