I've done this manually as an optimization on particularly hairy (and large) reports, retrieving a JSON string from the postgres query, then interpolating it in

I've done this manually as an optimization on particularly hairy (and large) reports, retrieving a JSON string from the postgres query, then interpolating it into a boilerplate string response. In a few, particularly pathological cases (that nonetheless were fairly common to run into in prod), the response time of the endpoint went from literal minutes to a few hundred milliseconds on a test server with unlimited response timeout (prod would have timed out after 60s). Most of the performance increase came from not requiring Ruby to parse strings into fat objects, then turn it back into a long string to go out the wire.