Implementing Domain-Driven Design

Scalability and Distribution

Since Aggregates don’t use direct references to other Aggregates but reference by identity, their persistent state can be moved around to reach large scale. Almost-infinite scalability is achieved by allowing for continuous repartitioning of Aggregate data storage, as explained by Amazon.com’s Pat Helland in his position paper “Life beyond Distributed Transactions: An Apostate’s Opinion” [Helland]. What we call Aggregate, he calls entity. But what he describes is still an Aggregate by any other name: a unit of composition that has transactional consistency. Some NoSQL persistence mechanisms support the Amazon-inspired distributed storage. These provide much of what [Helland] refers to as the lower, scale-aware layer. ...