From b25946e59cdaa54a01781cca2553a60a581773ef Mon Sep 17 00:00:00 2001
From: Tobias Grieger <tobias.b.grieger@gmail.com>
Date: Wed, 28 Oct 2020 13:06:50 +0100
Subject: [PATCH] tracing: improve comment on otSpan

Release note: None
---
 pkg/util/log/BUILD.bazel     |  1 +
 pkg/util/tracing/BUILD.bazel |  1 +
 pkg/util/tracing/span.go     | 11 ++++++++---
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/pkg/util/log/BUILD.bazel b/pkg/util/log/BUILD.bazel
index c835d17566da..3fa097003eae 100644
--- a/pkg/util/log/BUILD.bazel
+++ b/pkg/util/log/BUILD.bazel
@@ -145,6 +145,7 @@ go_test(
         "//vendor/github.com/kr/pretty",
         "//vendor/github.com/pmezard/go-difflib/difflib",
         "//vendor/github.com/stretchr/testify/assert",
+        "//vendor/github.com/stretchr/testify/require",
         "//vendor/golang.org/x/net/trace",
     ] + select({
         "@io_bazel_rules_go//go/platform:aix": [
diff --git a/pkg/util/tracing/BUILD.bazel b/pkg/util/tracing/BUILD.bazel
index 1e8fca620df2..c181e61562b2 100644
--- a/pkg/util/tracing/BUILD.bazel
+++ b/pkg/util/tracing/BUILD.bazel
@@ -6,6 +6,7 @@ go_library(
         "annotate.go",
         "annotate_nocgo.go",
         "grpc_interceptor.go",
+        "recording.go",
         "shadow.go",
         "span.go",
         "tags.go",
diff --git a/pkg/util/tracing/span.go b/pkg/util/tracing/span.go
index aad1cc2595d0..760b299112f9 100644
--- a/pkg/util/tracing/span.go
+++ b/pkg/util/tracing/span.go
@@ -145,10 +145,15 @@ func (s *crdbSpan) isRecording() bool {
 	return s != nil && atomic.LoadInt32(&s.recording) != 0
 }
 
+// otSpan is a span for an external opentracing compatible tracer
+// such as lightstep, zipkin, jaeger, etc.
 type otSpan struct {
-	// TODO(tbg): see if we can lose the shadowTr here and rely on shadowSpan.Tracer().
-	// Probably not - but worth checking.
-	// TODO(tbg): consider renaming 'shadow' -> 'ot' or 'external'.
+	// shadowTr is the shadowTracer this span was created from. We need
+	// to hold on to it separately because shadowSpan.Tracer() returns
+	// the wrapper tracer and we lose the ability to find out
+	// what tracer it is. This is important when deriving children from
+	// this span, as we want to avoid mixing different tracers, which
+	// would otherwise be the result of cluster settings changed.
 	shadowTr   *shadowTracer
 	shadowSpan opentracing.Span
 }