Fix gauge aggregation

[andreaswachowski]

I noticed that the aggregation-parameter for gauges did nothing in a multi-process setting (the pid-attribute was still present). This PR should fix that.

[ollym]

@Envek ?

[Envek]

Hey, thanks a lot for the pull request and sorry for long reply.

The problem I can see here is that aggregation option of Yabeda gauge was made to support official Prometheus client's aggregation setting which supports more modes than GitLab's Prometheus mmap client does. The missing one is most_recent mode which is used e.g. by yabeda-sidekiq here. If pass existing modes as is to prometheus-mmap then it will probably raise an error.

Most probably we will need to map existing values (sum to livesum at least) and just not pass most_recent. But let me think a bit about it. Details of your use case or your thoughts are more than welcome!

[ollym]

@Envek use case for us is switching to https://github.com/Shopify/pitchfork (from Puma) and we need to provide our own stats:

Yabeda.configure do

  group :pitchfork do
    gauge :workers, aggregation: :max, comment: 'Number of pitchfork workers'
    gauge :active_workers, aggregation: :max, comment: 'Number of active pitchfork workers'
    gauge :request_backlog, aggregation: :max,  comment: 'Number of requests waiting to be processed by a pitchfork worker'
  end

  collect do
    if defined?(Raindrops::Linux.tcp_listener_stats)
      if listener_address = Pitchfork.listener_names.first
        stats = Raindrops::Linux.tcp_listener_stats([listener_address])[listener_address]
        pitchfork.active_workers.set({}, stats.active)
        pitchfork.request_backlog.set({}, stats.queued)
      end

      pitchfork.workers.set({}, File.read("/proc/#{Process.ppid}/task/#{Process.ppid}/children").split.count - 1) if Process.ppid > 0
    end
  end
end

Problem is this results in something like this:

pitchfork_workers{pid="314"} 29
pitchfork_workers{pid="318"} 29
pitchfork_workers{pid="324"} 29
pitchfork_workers{pid="34"} 29
pitchfork_workers{pid="41"} 29
pitchfork_workers{pid="45"} 29

So instead of just 29 we have 174

[Envek]

Sorry for the late reply and thanks for heads up.

Merged and released in 0.4.0. Enjoy!