Eventing

This is the Couchbase Eventing engine. It is intended to allow associating user code with any event that occurs inside Couchbase Server. An event is a change in state of any element of the server. Initial focus is on data state changes, but future versions will bring ability to handle non-data event.

Eventing is a MDS enabled service, and will run user supplied code on nodes designated with Eventing role. The role supports linear scalability and online rebalance. The consistency model is same as the GSI model, which is ability to do unbounded consistency, and at-or-after consistency.

We use Google V8 to run user supplied Javascript code. we do not support full Javascript syntax, because the programming model we offer needs to automatically parallelize on multiple nodes to handle the volume of events. For example, no global variables are accessible in event handlers.

We add a number of extensions to Javascript to make it easy to work with Couchbase. For example, Couchbase Buckets appear as javascript maps, N1QL results can be iterated over using javascript iterators and a number of added functions allow event handlers to send messages, raise more events etc.