I have a small web application that uses Firestore for the data. I am currently storing around 8 million objects.
The data size in the Firestore database is 10 times bigger than it is in "raw" format (json files).
Reading this wiki I came to the conclusion that there is a high chance that the automatic indexes are guilty of the humongous size of the database.
I have read the indexing documentation and it says how to create and remove custom indexes from the console, but I haven't find a way of removing automatic indexes.
Since I am only doing direct access to the objects, I don't need fields indexing at all.