feat: add stats for serialization time in otlp exporter (#1628)

Co-authored-by: Francis Bogsanyi <[email protected]>

Author: plantfansam

exporter/otlp/lib/opentelemetry/exporter/otlp/exporter.rb

@@ -271,6 +271,7 @@ def backoff?(retry_count:, reason:, retry_after: nil) # rubocop:disable Metrics/
         end
 
         def encode(span_data) # rubocop:disable Metrics/MethodLength, Metrics/CyclomaticComplexity
+          start = Process.clock_gettime(Process::CLOCK_MONOTONIC)
           Opentelemetry::Proto::Collector::Trace::V1::ExportTraceServiceRequest.encode(
             Opentelemetry::Proto::Collector::Trace::V1::ExportTraceServiceRequest.new(
               resource_spans: span_data
@@ -298,6 +299,11 @@ def encode(span_data) # rubocop:disable Metrics/MethodLength, Metrics/Cyclomatic
         rescue StandardError => e
           OpenTelemetry.handle_error(exception: e, message: 'unexpected error in OTLP::Exporter#encode')
           nil
+        ensure
+          stop = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+          duration_ms = 1000.0 * (stop - start)
+          @metrics_reporter.record_value('otel.otlp_exporter.encode_duration',
+                                         value: duration_ms)
         end
 
         def as_otlp_span(span_data) # rubocop:disable Metrics/MethodLength, Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity

exporter/otlp/test/opentelemetry/exporter/otlp/exporter_test.rb

@@ -382,6 +382,17 @@
       _(result).must_equal(SUCCESS)
     end
 
+    it 'records metrics' do
+      metrics_reporter = Minitest::Mock.new
+      exporter = OpenTelemetry::Exporter::OTLP::Exporter.new(metrics_reporter: metrics_reporter)
+      stub_request(:post, 'http://localhost:4318/v1/traces').to_timeout.then.to_return(status: 200)
+      metrics_reporter.expect(:record_value, nil) { |m, _, _| m == 'otel.otlp_exporter.encode_duration' }
+      metrics_reporter.expect(:record_value, nil) { |m, _, _| m == 'otel.otlp_exporter.message.uncompressed_size' }
+      metrics_reporter.expect(:record_value, nil) { |m, _, _| m == 'otel.otlp_exporter.message.compressed_size' }
+      metrics_reporter.expect(:add_to_counter, nil) { |m, _, _| m == 'otel.otlp_exporter.failure' }
+      exporter.export([OpenTelemetry::TestHelpers.create_span_data])
+    end
+
     it 'retries on timeout' do
       stub_request(:post, 'http://localhost:4318/v1/traces').to_timeout.then.to_return(status: 200)
       span_data = OpenTelemetry::TestHelpers.create_span_data