I am able to add composite indexes to index.yaml file and get it to work without removing and reloading the data from datastore

Question

I thought that this was not possible and that you had to reload all the data if you added new indexes.

Is this supposed to happen?

Answer 1

When Cloud Datastore builds a new index, it includes any existing entities that match the index, so there's no need to update your existing data.

If, however, you have inserted entities with unindexed properties and decide you want to define indexes on those properties, then you need to update each of those entities to mark the property as indexed.