- Similar in nature to the nested model: both allow you to associate one entity with another
- Parent-Child linked documents will be stored in the same shard, possible trouble with data distribution
- With nested datatype all data lives within the scope of parent document
- With parent-child: parent and each child are indexed separately
- Children can be queried, updated, and deleted separately from the parent and from each other
- With large number of child documents parent-child indexing is more effective
- Child documents can be incorporated into query criteria and into the query results
- Parent-Child maps are stored in so called doc values quick in-memory processing and scalable split on disk
- There are still performance concerns voiced in Elastic documentation