You know how SELECT * can be bad for performance, right? Extra serialization/deserialization, more disc and network IO, no index-only scans etc 
(a good detailed read on this topic Reasons why SELECT * is bad for SQL performance | Tanel Poder Consulting).
I created a small gem to tackle exactly this problem - show unused selected columns. Works for controllers, ActiveJob and sidekiq jobs - GitHub - fatkodima/columns_trace: Find unnecessary selected database columns
The logged output looks like this:
ImportsController#create
1 User record: unused columns - "bio", "settings"; used columns - "id", "email", "name",
"account_id", "created_at", "updated_at"
↳ app/controllers/application_controller.rb:32:in `block in <class:ApplicationController>'
1 Account record: unused columns - "settings", "logo", "updated_at";
used columns - "id", "plan_id"
↳ app/controllers/application_controller.rb:33:in `block in <class:ApplicationController>'
10 Project records: unused columns - "description", "avatar", "url", "created_at", "updated_at";
used columns - "id", "user_id"
↳ app/models/user.rb:46: in `projects'
app/services/imports_service.rb:129: in `import_projects'
app/controllers/imports_controller.rb:49:in `index'
ImportProjectJob
1 User record: unused columns - "email", "name", "bio", "created_at", "updated_at";
used columns - "id", "settings"
↳ app/jobs/import_project_job.rb:23:in `perform'
1 Project record: unused columns - "description", "avatar", "settings", "created_at",
"updated_at"; used columns - "id", "user_id", "url"
↳ app/jobs/import_project_job.rb:24:in `perform'
