From ae6d29f4b144abc6634c307038d42beb4b5fa260 Mon Sep 17 00:00:00 2001
From: Damien Mathieu <42@dmathieu.com>
Date: Tue, 16 Jul 2024 09:22:04 +0200
Subject: [PATCH] Refactor Batch Processor benchmark to really test OnEnd
 (#5600)

This benchmark was not only testing the batch processor, since it was
starting a span, and ending it.
So the entire process of recording span was being accounted.

This changes the benchmark to only account for the batch processor being
tested, not the entire stack.

Before:
```
pkg: go.opentelemetry.io/otel/sdk/trace
BenchmarkSpanProcessor-10                         137320              8696 ns/op           11184 B/op        155 allocs/op
BenchmarkSpanProcessorVerboseLogging-10           135483              8881 ns/op           11184 B/op        155 allocs/op
PASS
ok      go.opentelemetry.io/otel/sdk/trace      3.984s
```

After:
```
pkg: go.opentelemetry.io/otel/sdk/trace
BenchmarkSpanProcessorOnEnd/batch:_10,_spans:_10-10              6055572               173.2 ns/op             0 B/op          0 allocs/op
BenchmarkSpanProcessorOnEnd/batch:_10,_spans:_100-10              684236              1733 ns/op               0 B/op          0 allocs/op
BenchmarkSpanProcessorOnEnd/batch:_100,_spans:_10-10             6930391               173.8 ns/op             0 B/op          0 allocs/op
BenchmarkSpanProcessorOnEnd/batch:_100,_spans:_100-10             677128              1731 ns/op               0 B/op          0 allocs/op
BenchmarkSpanProcessorVerboseLogging-10                           128823              9318 ns/op           11184 B/op        155 allocs/op
PASS
ok      go.opentelemetry.io/otel/sdk/trace      6.763s
```

I haven't touched the verbose logging benchmark, as I suppose a
benchmark with verbose logging could actually benefit from the entire
stack.
I also feel one benchmark testing the entire stack up to there could be
nice.
---
 sdk/trace/batch_span_processor_test.go | 43 ++++++++++++++++----------
 1 file changed, 26 insertions(+), 17 deletions(-)

diff --git a/sdk/trace/batch_span_processor_test.go b/sdk/trace/batch_span_processor_test.go
index d0720ff5de9..51fdd6b65db 100644
--- a/sdk/trace/batch_span_processor_test.go
+++ b/sdk/trace/batch_span_processor_test.go
@@ -627,23 +627,32 @@ func TestBatchSpanProcessorConcurrentSafe(t *testing.T) {
 	wg.Wait()
 }
 
-func BenchmarkSpanProcessor(b *testing.B) {
-	tp := sdktrace.NewTracerProvider(
-		sdktrace.WithBatcher(
-			tracetest.NewNoopExporter(),
-			sdktrace.WithMaxExportBatchSize(10),
-		))
-	tracer := tp.Tracer("bench")
-	ctx := context.Background()
-
-	b.ResetTimer()
-	b.ReportAllocs()
-
-	for i := 0; i < b.N; i++ {
-		for j := 0; j < 10; j++ {
-			_, span := tracer.Start(ctx, "bench")
-			span.End()
-		}
+func BenchmarkSpanProcessorOnEnd(b *testing.B) {
+	for _, bb := range []struct {
+		batchSize  int
+		spansCount int
+	}{
+		{batchSize: 10, spansCount: 10},
+		{batchSize: 10, spansCount: 100},
+		{batchSize: 100, spansCount: 10},
+		{batchSize: 100, spansCount: 100},
+	} {
+		b.Run(fmt.Sprintf("batch: %d, spans: %d", bb.batchSize, bb.spansCount), func(b *testing.B) {
+			bsp := sdktrace.NewBatchSpanProcessor(
+				tracetest.NewNoopExporter(),
+				sdktrace.WithMaxExportBatchSize(bb.batchSize),
+			)
+			snap := tracetest.SpanStub{}.Snapshot()
+
+			b.ResetTimer()
+			b.ReportAllocs()
+			for i := 0; i < b.N; i++ {
+				// Ensure the export happens for every run
+				for j := 0; j < bb.spansCount; j++ {
+					bsp.OnEnd(snap)
+				}
+			}
+		})
 	}
 }