add metrics otelcol_exporter_queue_capacity

Signed-off-by: Ziqi Zhao <zhaoziqi9146@gmail.com>

exporter/exporterhelper/obsreport.go

@@ -40,6 +40,7 @@ func init() {
 type instruments struct {
 	registry                    *metric.Registry
 	queueSize                   *metric.Int64DerivedGauge
+	queueCapacity               *metric.Int64DerivedGauge
 	failedToEnqueueTraceSpans   *metric.Int64Cumulative
 	failedToEnqueueMetricPoints *metric.Int64Cumulative
 	failedToEnqueueLogRecords   *metric.Int64Cumulative
@@ -55,6 +56,12 @@ func newInstruments(registry *metric.Registry) *instruments {
 		metric.WithLabelKeys(obsmetrics.ExporterKey),
 		metric.WithUnit(metricdata.UnitDimensionless))
 
+	insts.queueCapacity, _ = registry.AddInt64DerivedGauge(
+		obsmetrics.ExporterKey+"/queue_capacity",
+		metric.WithDescription("Current capacity of the retry queue (in batches)"),
+		metric.WithLabelKeys(obsmetrics.ExporterKey),
+		metric.WithUnit(metricdata.UnitDimensionless))
+
 	insts.failedToEnqueueTraceSpans, _ = registry.AddInt64Cumulative(
 		obsmetrics.ExporterKey+"/enqueue_failed_spans",
 		metric.WithDescription("Number of spans failed to be added to the sending queue."),

exporter/exporterhelper/queued_retry_inmemory.go

@@ -128,6 +128,12 @@ func (qrs *queuedRetrySender) start(context.Context, component.Host) error {
 		if err != nil {
 			return fmt.Errorf("failed to create retry queue size metric: %w", err)
 		}
+		err = globalInstruments.queueCapacity.UpsertEntry(func() int64 {
+			return int64(qrs.queue.Capacity())
+		}, metricdata.NewLabelValue(qrs.fullName))
+		if err != nil {
+			return fmt.Errorf("failed to create retry queue capacity metric: %w", err)
+		}
 	}
 
 	return nil