Simple Rails Monitoring

cleanup_job.rb

# services/monitoring/cleanup_service.rb
class Monitoring::CleanupService
  def self.run
    Monitoring::Measurement.where("recorded_at < ?", 3.months.ago).delete_all
  end
end
# let this service run nightly

delayed_job_extension.rb

# models/monitoring/job.rb
class Monitoring::Job < Monitoring::Measurement
  # value shows how long the job took in seconds
end

# config/initializers/monitoring.rb
class MonitoringPlugin < Delayed::Plugin
  callbacks do |lifecycle|
    lifecycle.around(:perform) do |worker, job, &block|
      return if job.nil? || block.nil?
      duration = Benchmark.realtime do
        block.call(worker)
      end

      Monitoring::Job.create!(
        recorded_at: Time.current,
        subject: job.name,
        value: duration,
        details: {})
    rescue => e
      # notify exception
    end
  end
end
Delayed::Worker.plugins << MonitoringPlugin

# example data
# | id | type            | recorded_at         | subject       | value | details |
# |----|-----------------|---------------------|---------------|-------|---------|
# |  1 | Monitoring::Job | 2021-03-15 11:44:00 | SomeJob#run   | 0.017 | {}      |
# |  2 | Monitoring::Job | 2021-03-15 11:44:00 | OtherJob.send | 1.074 | {}      |

mail_extension.rb

# models/monitoring/mail.rb
class Monitoring::Mail < Monitoring::Measurement
  store_accessor :details, :to
  # value shows how long the sending took in seconds
end

# config/initializers/monitoring.rb
ActiveSupport::Notifications.subscribe 'deliver.action_mailer' do |name, started, finished, unique_id, data|
  Monitoring::Mail.create!(recorded_at: started, subject: "#{data[:mailer]}", value: finished - started, to: data[:to])
rescue => e
  # notify exception
end

# example data:
# | id | type             | recorded_at         | subject | value | details                             |
# |----|------------------|---------------------|---------|-------|-------------------------------------|
# |  1 | Monitoring::Mail | 2021-03-13 11:38:00 |         |  0.06 | {"to": ["development@example.net"]} |
# |  2 | Monitoring::Mail | 2021-03-13 11:38:00 |         |  0.05 | {"to": ["development@example.net"]} |
# |  3 | Monitoring::Mail | 2021-03-13 11:38:00 |         |  0.05 | {"to": ["development@example.net"]} |

table_size_extension.rb

# value shows how big the table is in MB
class Monitoring::TableSize < Monitoring::Measurement
  store_accessor :details, :index_size, :data_size
end

# services/monitoring/table_size_recorder_service.rb
class Monitoring::TableSizeRecorderService
  def self.run
    query = 'SELECT relname AS table_name, pg_total_relation_size(relid) AS total_size, pg_indexes_size(relid) AS index_size, pg_relation_size(relid) AS data_size FROM pg_catalog.pg_statio_user_tables'
    ActiveRecord::Base.connection.execute(query).each do |row|
      Monitoring::TableSize.create!(
        recorded_at: Time.current,
        subject:     row['table_name'],
        value:       row['total_size'] / 1_048_576.0, # mb
        index_size:  row['index_size'] / 1_048_576.0,
        data_size:   row['data_size']  / 1_048_576.0
      )
    end
  end
end
# let this service run nightly

# example data:
# | id | type                  | recorded_at         | subject  | value  | details                                    |
# |----|-----------------------|---------------------|----------|--------|--------------------------------------------|
# | 1  | Monitoring::TableSize | 2021-03-15 11:47:00 | users    |   0.59 | {"data_size":   0.414, "index_size": 0.15} |
# | 2  | Monitoring::TableSize | 2021-03-15 11:47:00 | articles |  14.48 | {"data_size":   9.703, "index_size": 4.75} |
# | 3  | Monitoring::TableSize | 2021-03-15 11:47:00 | sausages | 190.85 | {"data_size": 150.296, "index_size": 40.5} |

http://tomrothe.de/posts/dead-simple-rails-monitoring.html