Dropping traces before they are exported

[knjoroge]

Hello,

We are using the ruby opentelemetry gems for ruby

opentelemetry-instrumentation-redis (~> 0.21.1)

We have some PING traces that are a bit noisy. Is there any way to drop or filter these traces out before they are exported by the collector?

[arielvalentin]

I don't think so. The otel-collector-contrib repo does not seem support filtering spans and I think there is really only a desire to filter entire traces.

open-telemetry/opentelemetry-collector#2310

It looks like you'll need a custom span processor.

Another option may be, if you're interested, is submitting a PR to redis auto-instrumentation to filter specific queries. I imagine they it would be similar to how the Rack auto-instrumentation filters by path.

[fbogsany]

open-telemetry/opentelemetry-collector-contrib#6341 added support for filtering spans, which would be perfect for what you want here. It was approved, but auto-closed as stale before it was merged 😞 .

You can filter these spans at source either with a custom span processor, as @arielvalentin suggests, or with a custom sampler. E.g.

class DropPingSampler
  DROP_IT = OpenTelemetry::SDK::Trace::Samplers::ALWAYS_OFF

  def initialize(delegate)
    @delegate = delegate
  end

  def description
    'DropPingSampler'
  end

  def should_sample?(trace_id:, parent_context:, links:, name:, kind:, attributes:)
    delegate = if name == 'PING' && attributes&.dig('db.system') == 'redis'
      DROP_IT
    else
      @delegate
    end
    delegate.should_sample?(trace_id: trace_id, parent_context: parent_context, links: links, name: name, kind: kind, attributes: attributes)
  end
end