On the composability of the Riak DT map: expanding from embedded to multi-key structures

The Riak DT library [2] provides a composable, convergent replicated dictionary called the Riak DT map, designed for use in the Riak [1] replicated data store. This data type provides the ability for the composition of conflict-free replicated data types (CRDT) [7] through embedding. Composition by embedding works well when the total object size of the composed CRDTs is small, however suffers a performance penalty as object size increases. The root of this problem is based in how replication is achieved in the Riak data store using Erlang distribution. [4] We propose a solution for providing an alternative composition mechanism, composition by reference, which provides support for arbitrarily large objects while ensuring predictable performance and high availability. We explore the use of this new composition mechanism by examining a common use case for the Riak data store.