Suggestion: Track ActiveRecord connection pool stats

[rainerborene]

A suggestion for a new probe on this library by using this piece of code: ActiveRecord::Base.connection_pool.stat

[tombruijn]

The data not being in the previous comment was because of preload_app! loading AppSignal in the Puma primary process. There the probes didn't have access to the connection pool data. We added docs for how to configure AppSignal when using this Puma config: https://docs.appsignal.com/ruby/integrations/puma.html#usage-with-preload_app

[krystof-k]

One more update from me. Based on @tombruijn findings, here is my final setup for the ActiveRecord connection pool probe, working both in Puma workers and everywhere else:

intiializers/appsignal.rb rests the same:

Appsignal::Probes.register(:active_record_connection_pool, lambda do
  ActiveRecord::Base.connection_pool.stat.each do |key, value|
    hostname = Appsignal.config[:hostname] || Socket.gethostname
    Appsignal.set_gauge("active_record_connection_pool_#{key}", value, {hostname:})
  end
end)

config/puma.rb is a little cleaner, however it is still required to re-register the probe to include the Puma worker number:

preload_app!

before_fork do
  # Stop AppSignal probes in the Puma main process
  Appsignal::Probes.stop
  # Deregister AppSignal probe from the Puma main process
  Appsignal::Probes.unregister(:active_record_connection_pool)
end

on_worker_boot do |worker_index|
  # Register the AppSignal probe in the Puma worker process
  Appsignal::Probes.register(:active_record_connection_pool, lambda do
    ActiveRecord::Base.connection_pool.stat.each do |key, value|
      hostname = Appsignal.config[:hostname] || Socket.gethostname
      Appsignal.set_gauge("active_record_connection_pool_#{key}", value, {hostname:, process: worker_index})
    end
  end)
  # Start AppSignal probes in the Puma worker process
  Appsignal::Probes.start
end