Queries other than document reads
For queries other than document reads, such as a request for a list of collection IDs, you are billed for one document read. If fetching the complete set of results requires more than one request (for example, if you are using pagination), you are billed once per request.
I can not find any information of how to perform such queries - to get only IDs.
Anyone knows how?
You can get the collection IDs using the REST API. The documentation is here
You can also return an array of collection IDs with
documentRef.getCollections()
as detailed here