Class: Findbug::Performance::Instrumentation

Inherits:
Object
  • Object
show all
Defined in:
lib/findbug/performance/instrumentation.rb

Overview

Instrumentation subscribes to Rails’ ActiveSupport::Notifications.

WHAT IS ActiveSupport::Notifications?

Rails has a built-in pub/sub system for internal events. Every time something interesting happens, Rails publishes a notification:

- sql.active_record → Database queries
- process_action.action_controller → HTTP requests
- render_template.action_view → View rendering
- cache_read.active_support → Cache operations

Any code can subscribe to these events:

ActiveSupport::Notifications.subscribe("sql.active_record") do |event|
  puts "Query took #{event.duration}ms"
end

This is how Rails’ request logs, performance gems, and APM tools work. We subscribe to capture timing data for our dashboard.

WHY NOT MIDDLEWARE FOR PERFORMANCE?

Middleware only sees the request start and end. It can’t see:

  • Individual SQL queries

  • Which view took how long

  • Cache hits/misses

Notifications give us granular visibility into the request lifecycle.

Constant Summary collapse

SUBSCRIPTIONS = 
[
  "process_action.action_controller",
  "sql.active_record",
  "render_template.action_view",
  "render_partial.action_view",
  "cache_read.active_support",
  "cache_write.active_support"
].freeze

Class Method Summary collapse

Class Method Details

.setup! ⇒ Object

Set up all instrumentation subscriptions

Called once during Rails initialization (via Railtie).



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# File 'lib/findbug/performance/instrumentation.rb', line 54

def setup!
  return if @setup_complete
  return unless Findbug.config.performance_enabled

  subscribe_to_requests
  subscribe_to_queries
  subscribe_to_views
  subscribe_to_cache

  @setup_complete = true
  Findbug.logger.debug("[Findbug] Performance instrumentation enabled")
end

.teardown! ⇒ Object

Tear down subscriptions (for testing)



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# File 'lib/findbug/performance/instrumentation.rb', line 68

def teardown!
  @subscriptions&.each do |subscriber|
    ActiveSupport::Notifications.unsubscribe(subscriber)
  end
  @subscriptions = []
  @setup_complete = false
end