BatchSpanProcessor: Exporter error handling does not provide useful information

[hibachrach]

If an Exporter returns a FAILURE status, the BatchSpanProcessor calls OpenTelemetry.handle_error with a new exception. But that exception doesn't tell you anything about what happened: all we get back is "Unable to export 90 spans" or some such because it just instantiated the error based on a return value--there's no raising or deeper stack trace (afaict).

Thanks again for all of your work on OTel!

[ericmustin]

@hibachrach sorry for the delay here. There's a bit of tech debt here for sure, at the time we'd hit this issue originally at $job-2, otel metrics were unstable, and we were a statsd shop, so we exposed a not very well documented MetricsReporter that you can define (otherwise it just no-ops iirc) and which provides some extra debugging info about the processors and exporters, which you can then theoretically provide your own metrics client to export to your backend of choice, or logger, etc.

opentelemetry-ruby/sdk/lib/opentelemetry/sdk/trace/export/metrics_reporter.rb

Lines 18 to 29 in 23c5aaf

	# @example
	# module MetricsReporter
	# def add_to_counter(metric, increment: 1, labels: {})
	# StatsD.increment(metric, increment, labels, no_prefix: true)
	# end
	# def record_value(metric, value:, labels: {})
	# StatsD.distribution(metric, value, labels, no_prefix: true)
	# end
	# def observe_value(metric, value:, labels: {})
	# StatsD.gauge(metric, value, labels, no_prefix: true)
	# end
	# end

And you can see its use within the BSP here

opentelemetry-ruby/sdk/lib/opentelemetry/sdk/trace/export/batch_span_processor.rb

Line 66 in 1279826

@metrics_reporter = metrics_reporter || OpenTelemetry::SDK::Trace::Export::MetricsReporter

Anyway, I realize that's very far from a first class feature, this is probably something we'd be open to revisiting or reworking given capacity or contributions from the community :)