Graylog2 is an open source syslog implementation that stores your logs in ElasticSearch. It consists of a server written in Java that accepts your syslog messages via TCP or UDP and stores it in the database. The second part is a Ruby on Rails web interface that allows you to view the log messages. This fork of graylog2 is used by odnoklassniki internally, so it contain patches targeted at support of fast operation and large number of logging hosts.