Add local batched Git blob reader

internal/git/performance_test.go

@@ -0,0 +1,59 @@
+package git
+
+import (
+	"context"
+	"runtime"
+	"testing"
+)
+
+func BenchmarkPerformanceBlobReader(b *testing.B) {
+	fixture := newRemoteFixture(b)
+	objectID := gitText(b, fixture.work, "rev-parse", "HEAD:source.txt")
+	const expectedBytes = int64(len("candidate"))
+
+	b.Run("new-session-per-read", func(b *testing.B) {
+		b.ReportAllocs()
+		b.SetBytes(expectedBytes)
+		b.ResetTimer()
+		b.ReportMetric(float64(expectedBytes), "bytes/op")
+		b.ReportMetric(1, "blobs/op")
+		for i := 0; i < b.N; i++ {
+			reader := NewBlobReader(context.Background(), fixture.work)
+			contents, err := reader.Read(context.Background(), objectID)
+			if err != nil {
+				b.Fatal(err)
+			}
+			if int64(len(contents)) != expectedBytes {
+				b.Fatalf("read %d bytes, want %d", len(contents), expectedBytes)
+			}
+			if err := reader.Close(); err != nil {
+				b.Fatal(err)
+			}
+			runtime.KeepAlive(contents)
+		}
+	})
+
+	b.Run("shared-session", func(b *testing.B) {
+		reader := NewBlobReader(context.Background(), fixture.work)
+		b.Cleanup(func() {
+			if err := reader.Close(); err != nil {
+				b.Error(err)
+			}
+		})
+		b.ReportAllocs()
+		b.SetBytes(expectedBytes)
+		b.ResetTimer()
+		b.ReportMetric(float64(expectedBytes), "bytes/op")
+		b.ReportMetric(1, "blobs/op")
+		for i := 0; i < b.N; i++ {
+			contents, err := reader.Read(context.Background(), objectID)
+			if err != nil {
+				b.Fatal(err)
+			}
+			if int64(len(contents)) != expectedBytes {
+				b.Fatalf("read %d bytes, want %d", len(contents), expectedBytes)
+			}
+			runtime.KeepAlive(contents)
+		}
+	})
+}