Siren Platform User Guide

How does Siren Federate join compare with parent-child

The Siren Federate join is similar in nature to the Parent-Child (https://www.elastic.co/guide/en/elasticsearch/guide/current/parent-child.html) feature of Elasticsearch: they perform a join at query-time. However, there are important differences between them:

  • The parent document and all of its children must live on the same shard, which limits its flexibility. The Siren Federate join removes this constraint and is therefore more flexible: it allows joining documents across shards and across indices.

  • Thanks to the data locality of the Parent-Child model, joins are faster and more scalable. The Siren Federate join on the contrary needs to transfer data across the network to compute joins across shards, limiting its scalability and performance.

There is no “one size fits all” solution to this problem, and you need to understand your requirements to choose the proper solution. As a basic rule, if your data model and data relationships are purely hierarchical (or can be mapped to a purely hierarchical model), then the Parent-Child model might be more appropriate. If on the contrary you need to query both directions of a data relationship, then the Siren Federate join might be more appropriate.