Firestore: How are "reads" calculated for the quota?

Question

I don't understand the way "firestore" counts the reads for the quota and billing.

Example: I have a collection with 200'000 documents. Every document has a timestamp as attribute. Now I would like to get all documents within the last hour. So I create a query which gives me back all documents with "timestamp > now()-60 minutes". The result is a set of 10 documents. Does Firestore counts 10 document reads or 200'000 documents read for this? I would like to build a query that read a document always once (fetch, not real time).

I assume that firestore is only at the first view a cheaper solution than with other solution (e.g. google cloud sql, aws etc).

Answer 1

To allow that query, you will need to have an index on timestamp. Firestore uses that index to determine what documents to return. So this would count as 10 document reads.