Learning Elasticsearch

How parent-child works internally

Elasticsearch stores the parent and child documents in the same shard. Having both the parent and child documents in the same shard will make the has_parent and has_child queries possible. The parent ID is used to determine the shard to which the child document belongs to. To index or retrieve a child document, you need the parent ID. We index a child document (product_review) as shown here:

 #Child Document POST chapter7/product_review/?parent=1 {"user_id" : "reviewer1", "comment" : "One of the best phones in the market"}

When using parent-child, you are trading indexing performance for query performance. Internally, Elasticsearch has to maintain a join between the parent documents and child documents. ...