Caching considerations

[CasperWA]

Should we cache the results returned from a gateway's databases according to the query?
If yes, this could be done in different ways, either on a per gateway basis, or in a Mongo collection per database or similar that each gateway can then query. The latter would not demand as much space, and is to be preferred.
We would need to ensure the same result can be found regardless of the order of the query parameters.
Persistence time?

What is the level of caching that should eventually be implemented?
We could simply only cache meta data, like data_available, etc., or cache whole entries/responses from each database.

Gateway response caching.
For the expected POST endpoints for querying gateways, how long should the responses be cached for to be re-retrieved?
Should regular GET query requests to gateways also be cached?