fix: Do not log error when there are no metrics to export

[wsmoak]

When collected_metrics is empty, result_code does not get set, and so report_result would log an error with a blank code.

Since the exporters already log if they encounter problems, there is no need to repeat the error logging here.

Reported by: @utay

Related to: #1947 and #1888

[arielvalentin]

Would a case statement here be better and add a debug message for the default?

[wsmoak]

I was going for the simplest fix that could possibly work. To cover all the cases, I think it would be...

          def report_result(result_code)
            case result_code
            when Export::SUCCESS
              OpenTelemetry.logger.debug 'Successfully exported metrics'
            when Export::FAILURE
              OpenTelemetry.handle_error(exception: ExportError.new('Unable to export metrics'))
              OpenTelemetry.logger.error("Result code: #{result_code}")
            when Export::TIMEOUT
              OpenTelemetry.handle_error(exception: ExportError.new('Export operation timed out'))
              OpenTelemetry.logger.error("Result code: #{result_code}")
            when nil
              OpenTelemetry.logger.debug 'No metrics to export'
            else
              OpenTelemetry.logger.warn "Unknown result code when exporting metrics: #{result_code}"
            end
          end

Would you prefer that instead?

[arielvalentin]

I think so yes.

Although handle_error would be enough for the error cases since it logs by default.

So I would suggest either choosing to use handle_error or logger in those cases but not both.

[wsmoak]

I agree that logging the result code doesn't add much value, I removed it.

[wsmoak]

Tested locally. Started the app, waited a bit and recorded a data point, then turned off the collector. (I am not sure how to make a timeout happen.)

D, [2025-11-03T19:22:15.205141 #59504] DEBUG -- : No metrics to export
D, [2025-11-03T19:23:15.223879 #59504] DEBUG -- : Successfully exported metrics
W, [2025-11-03T19:24:39.281246 #59504]  WARN -- : SystemCallError in MetricsExporter#send_bytes
E, [2025-11-03T19:24:39.284574 #59504] ERROR -- : OpenTelemetry error: Unable to export metrics

[arielvalentin]

Something to note here is that since this was not an exception then it will be missing a backtrace and that may confuse someone who is trying to handle the error:

irb(main):001> e = StandardError.new("bad")
=> #<StandardError: bad>
irb(main):002> e.backtrace
=> nil

The handle_error message does not need to have an exception: parameter and in this case may only need a message:.

Then again when I look at the exporter there is already a set of diagnositc errors there:

https://github.com/wsmoak/opentelemetry-ruby/blob/7419ef5888b488dcf2fbee769ae662eb7562c70b/exporter/otlp-metrics/lib/opentelemetry/exporter/otlp/metrics/metrics_exporter.rb#L136

So I guess my follow up question is... why does this also need to report errors in addition to the exporters. Is there some nuance I am missing?

[wsmoak]

All I really wanted was the success message. :)

I was following the pattern that Kayla set in the BLRP:

opentelemetry-ruby/logs_sdk/lib/opentelemetry/sdk/logs/export/batch_log_record_processor.rb

Lines 194 to 201 in 6f70825

	def report_result(result_code, batch)
	if result_code == SUCCESS
	OpenTelemetry.logger.debug("Successfully exported #{batch.size} log records")
	else
	OpenTelemetry.handle_error(exception: ExportError.new("Unable to export #{batch.size} log records"))
	OpenTelemetry.logger.error("Result code: #{result_code}")
	end
	end

I can remove the logging for errors, and assume the thing that returned the error has already logged it.

[wsmoak]

... and it collapses down to only logging the success message. Since there is no error logging, the nil value doesn't accidentally fall into it. Problem solved!

[wsmoak]

Tested running locally. The only output now (again with then without a collector running) is:

D, [2025-11-03T20:34:30.377782 #58928] DEBUG -- : Successfully exported metrics
W, [2025-11-03T20:35:56.420999 #58928]  WARN -- : SystemCallError in MetricsExporter#send_bytes