I have a database table cars that has close to 500k records. I was facing issues with long loading times to load data from this table.

@cars = Car.order('created_at DESC').paginate(page: params[:page], per_page: 100)

It took anywhere between 30-40 seconds to load and display @cars in the browser. I started optimizing it, eg. eliminating fetching information from tables with relation (eg. instead of car.photos.count -> car.total_photos).

Currently, it takes about 5 seconds to load this data. Below is a screenshot from rake mini profiler:

What surprises me is that the query on the screenshot, SELECT COUNT(*) FORM cars, takes about 3.7 seconds. The line 258 references on the screenshot is from pagination:

<%= page_entries_info @cars %>

When I check the indices on the cars table (select * from pg_indexes where tablename = 'cars'), I see the following:

CREATE UNIQUE INDEX cars_pkey ON public.cars USING btree (id)
CREATE INDEX index_cars_on_car_type ON public.cars USING btree (car_type)
CREATE INDEX index_cars_on_created_at ON public.cars USING btree (created_at)

What are the further possibilities to optimize it?