Recall that there are built-in indices in Datastore on every property of every entity. This only applies to individual properties, but there are also composite indices. These allow the indexing of multiple property values all at once. If you are absolutely certain that a property will never be queried, you can explicitly exclude it from full indexing, which might give you some performance benefits, particularly in write operations where you don't want to be updating unnecessary indices.
The way Datastore works, every query will be evaluated using something known as its perfect index. The perfect index is an interesting concept. Given a query, the perfect index is that index which will most optimally return the query's results. The perfect index is evaluated based on the following conditions:
- If there is an equality filtering condition...