Why do I have Rails views overhead when handling API requests? - ruby-on-rails

Question

I noticed in my logs that when I'm hitting API endpoints, the rails built in profiling is reporting that it is spending some time in "views" (heroku extra logging info removed):
[2021-08-06T21:04:20.864743 #32] INFO -- : Started POST "/api/v1/places_in_bounds" for 24.184.254.41 at 2021-08-06 21:04:20 +0000
[2021-08-06T21:04:20.865565 #32] INFO -- : Processing by Api::V1::PlacesController#in_bounds as */*
[2021-08-06T21:04:20.865629 #32] INFO -- : Parameters: {"place"=>{"east"=>-38.800911000000006, "north"=>62.13593387702106, "south"=>-109.113411, "west"=>9.516666266458477}}
[2021-08-06T21:04:20.903245 #32] INFO -- : Completed 200 OK in 37ms (Views: 26.8ms | ActiveRecord: 2.3ms | Allocations: 28475)
...but I'm not rendering any views! It's an API endpoint, not an erb. What's going on? Are my jsonapi-serializer serializers counted as views? Short of cracking open rails itself or profiling the ruby interpreter, it's not obvious to me what's going on. It's not a huge overhead (usually much less than 50%), but presumably the answer will be useful to others!

Answer 1

Short answer is yes your JSON serialisers are counted, because you call render in your controller.
Both ActionController::Base and ActionController::API include ActionController::Instrumentation, which wraps render in a benchmark:
def render(*)
render_output = nil
self.view_runtime = cleanup_view_runtime do
Benchmark.ms { render_output = super }
end
render_output
end
So, regardless of what format you are rendering, it captures and logs the runtime:
def log_process_action(payload) #:nodoc:
messages, view_runtime = [], payload[:view_runtime]
messages << ("Views: %.1fms" % view_runtime.to_f) if view_runtime
messages
end