开务分布式数据库 Tracing（二）—— 源码解析

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按照【开务数据库 Tracing（一）】介绍的使用 opentracing 要求，本文着重介绍开务数据库(原：云溪数据库) Tracing 模块中是如何实现 Span，SpanContexts 和 Tracer 的。

Part 1 - Tracing 模块调用关系

1.1 Traincg 模块包含的文件列表

Tracer.go ：定义了opentracing 中的trace相关接口的实现。

Tracer_span.go ：定义了opentracing中的span 相关操作的实现。

Tags.go ：定义了 opentracing中关于tags的相关接口。

Shadow.go ：不是opentracing中的概念，这里主要实现与zipkin的通信，用于tracing 信息推送到外部的zipkin中。

1.2 各个文件之间的调用关系

在 cluster_settings.go 中会创建 tracer，供全局使用，其他模块中使用这个 Tracer 实现 span 的创建和其他操作，例如设定 span 名称、设定 tag 、增加 log 等操作。

Part 2 - Opentracing
在开务数据库中的实现
以下是只是列出了部分接口实现，并非全部。

2.1 Span 接口实现：

GetContext 实现：API 用于获取 Span 中的 SpanContext，主要功能是先创建一个 map[string]string 类型的 baggageCopy, 将 span 中的 mu.Baggage 读出写入 baggageCopy，创建新的 spanContext，并且返回。

func (s *span) Context() opentracing.SpanContext {
   s.mu.Lock()
   defer s.mu.Unlock()
   baggageCopy := make(map[string]string, len(s.mu.Baggage))
   for k, v := range s.mu.Baggage {
      baggageCopy[k] = v
   }
   sc := &spanContext{
      spanMeta: s.spanMeta,
      Baggage:  baggageCopy,
   }
   if s.shadowTr != nil {
      sc.shadowTr = s.shadowTr
      sc.shadowCtx = s.shadowSpan.Context()
   }

   if s.isRecording() {
      sc.recordingGroup = s.mu.recordingGroup
      sc.recordingType = s.mu.recordingType
   }
   return sc
}

Finished 实现：API 用于结束一个 Span 的记录和追踪。​​​​​​

func (s *span) Finish() {
   s.FinishWithOptions(opentracing.FinishOptions{})
}

SetTag 实现：用于向指定的 Span 添加 Tag 信息。

func (s *span) SetTag(key string, value interface{}) opentracing.Span {
   return s.setTagInner(key, value, false /* locked */)
}

Log 实现：用于向指定的 Span 添加 Log 信息。

func (s *span) LogKV(alternatingKeyValues ...interface{}) {
   fields, err := otlog.InterleavedKVToFields(alternatingKeyValues...)
   if err != nil {
      s.LogFields(otlog.Error(err), otlog.String("function", "LogKV"))
      return
   }
   s.LogFields(fields...)
}

SetBaggageItem 实现：用于向指定的 Span 增加 Baggage 信息，主要是用于跨进程追踪使用。

func (s *span) SetBaggageItem(restrictedKey, value string) opentracing.Span {
   s.mu.Lock()
   defer s.mu.Unlock()
   return s.setBaggageItemLocked(restrictedKey, value)
}

BaggageItem 实现：用于获取指定的 Baggage 信息。

func (s *span) BaggageItem(restrictedKey string) string {
   s.mu.Lock()
   defer s.mu.Unlock()
   return s.mu.Baggage[restrictedKey]
}

SetOperationName 实现：用于设定 Span 的名称。

func (s *span) SetOperationName(operationName string) opentracing.Span {
 if s.shadowTr != nil {
  s.shadowSpan.SetOperationName(operationName)
 }
 s.operation = operationName
 return s
}

Tracer 实现：用于获取 Span 属于哪个 Tracer。

// Tracer is part of the opentracing.Span interface.
func (s *span) Tracer() opentracing.Tracer {
 return s.tracer

}

2.2 SpanContext 接口实现：

ForeachBaggageItem 实现：用于遍历 spanContext 中的 baggage 信息。

func (sc *spanContext) ForeachBaggageItem(handler func(k, v string) bool) {
   for k, v := range sc.Baggage {
      if !handler(k, v) {
         break
      }
   }
}

2.3 Tracer 接口实现：

Inject 实现：用于向 carrier 中注入 SpanContext 信息

// Inject is part of the opentracing.Tracer interface.
func (t *Tracer) Inject(
   osc opentracing.SpanContext, format interface{}, carrier interface{},
) error {
 ……

   // We only
support the HTTPHeaders/TextMap format.
   if format != opentracing.HTTPHeaders && format != opentracing.TextMap {
      return opentracing.ErrUnsupportedFormat
   }

   mapWriter, ok := carrier.(opentracing.TextMapWriter)
   if !ok {
      return opentracing.ErrInvalidCarrier
   }

   sc, ok := osc.(*spanContext)
   if !ok {
      return opentracing.ErrInvalidSpanContext
   }

   mapWriter.Set(fieldNameTraceID, strconv.FormatUint(sc.TraceID, 16))
   mapWriter.Set(fieldNameSpanID, strconv.FormatUint(sc.SpanID, 16))

   for k, v := range sc.Baggage {
      mapWriter.Set(prefixBaggage+k, v)
   }

  ……
   return nil
}

Extract 实现：用于从 carrier 中抽取出 SpanContext 信息。

func (t *Tracer) Extract(format interface{}, carrier interface{}) (opentracing.SpanContext, error) {
   // We only
support the HTTPHeaders/TextMap format.
   if format != opentracing.HTTPHeaders && format != opentracing.TextMap {
      return noopSpanContext{}, opentracing.ErrUnsupportedFormat
   }

   mapReader, ok := carrier.(opentracing.TextMapReader)
   if !ok {
      return noopSpanContext{}, opentracing.ErrInvalidCarrier
   }

   var sc spanContext
 ……

   err :=
mapReader.ForeachKey(func(k, v string) error {
      switch k = strings.ToLower(k); k {
      case fieldNameTraceID:
         var err error
         sc.TraceID, err = strconv.ParseUint(v, 16, 64)
         if err != nil {
            return opentracing.ErrSpanContextCorrupted
         }
      case fieldNameSpanID:
         var err error
         sc.SpanID, err = strconv.ParseUint(v, 16, 64)
         if err != nil {
            return opentracing.ErrSpanContextCorrupted
         }
      case fieldNameShadowType:
         shadowType = v
      default:
         if strings.HasPrefix(k, prefixBaggage) {
            if sc.Baggage == nil {
               sc.Baggage = make(map[string]string)
            }
            sc.Baggage[strings.TrimPrefix(k, prefixBaggage)] = v
         } else if strings.HasPrefix(k, prefixShadow) {
            if shadowCarrier == nil {
               shadowCarrier = make(opentracing.TextMapCarrier)
            }
            // We build a
shadow textmap with the original shadow keys.
            shadowCarrier.Set(strings.TrimPrefix(k, prefixShadow), v)
         }
      }
      return nil
   })
   if err != nil {
      return noopSpanContext{}, err
   }
   if sc.TraceID == 0 &&
sc.SpanID == 0 {
      return noopSpanContext{}, nil
   }

   ……
   return &sc, nil
}

StartSpan 接口实现：用于创建一个新的 Span，可根据传入不同 opts 来实现不同 Span 的初始化。

func (t *Tracer) StartSpan(
   operationName string, opts ...opentracing.StartSpanOption,
) opentracing.Span {
   // Fast paths to
avoid the allocation of StartSpanOptions below when tracing
   // is disabled: if we have no options
or a single SpanReference (the common
   // case) with a noop context, return a
noop span now.
   if len(opts) == 1 {
      if o, ok := opts[0].(opentracing.SpanReference); ok {
         if IsNoopContext(o.ReferencedContext) {
            return &t.noopSpan
         }
      }
   }

   shadowTr := t.getShadowTracer()
   ……

   return s
}

2.4 noop span 实现：

noop span 实现：使监控代码不依赖 Tracer 和 Span 的返回值，防止程序异常退出。

type noopSpan struct {
   tracer *Tracer
}

var _ opentracing.Span = &noopSpan{}

func (n *noopSpan) Context() opentracing.SpanContext                       { return noopSpanContext{} }
func (n *noopSpan) BaggageItem(key string) string                          { return "" }
func (n *noopSpan) SetTag(key string, value interface{}) opentracing.Span  { return n }
func (n *noopSpan) Finish()                                               {}
func (n *noopSpan) FinishWithOptions(opts opentracing.FinishOptions)      {}
func (n *noopSpan) SetOperationName(operationName string) opentracing.Span { return n }
func (n *noopSpan) Tracer() opentracing.Tracer                             { return n.tracer }
func (n *noopSpan) LogFields(fields ...otlog.Field)                        {}
func (n *noopSpan) LogKV(keyVals ...interface{})                           {}
func (n *noopSpan) LogEvent(event string)                                 {}
func (n *noopSpan) LogEventWithPayload(event string, payload interface{})  {}
func (n *noopSpan) Log(data opentracing.LogData)                           {}

func (n *noopSpan) SetBaggageItem(key, val string) opentracing.Span {
   if key == Snowball {
      panic("attempting to set Snowball on a noop span; use the Recordable option
to StartSpan")
   }
   return n
}

Part3 - 开务数据库中

Opentracing 简单使用示例

3.1 开启 Tracer Recording 测试

开务数据库中 开始创建的 span 均是 no operator span, 需要手动调用 StartRecording, 将 span 转换为可 record 状态，才能正常对 span 进行操作。

func TestTracerRecording(t *testing.T) {
 tr := NewTracer()

 noop1 := tr.StartSpan("noop")
 if _, noop := noop1.(*noopSpan); !noop {
  t.Error("expected noop span")
 }
 noop1.LogKV("hello", "void")

 noop2 := tr.StartSpan("noop2", opentracing.ChildOf(noop1.Context()))
 if _, noop := noop2.(*noopSpan); !noop {
  t.Error("expected noop child span")
 }
 noop2.Finish()
 noop1.Finish()

 s1 := tr.StartSpan("a", Recordable)
 if _, noop := s1.(*noopSpan); noop {
  t.Error("Recordable (but not recording) span should not be noop")
 }
 if !IsBlackHoleSpan(s1) {
  t.Error("Recordable span should be black hole")
 }

 // Unless recording is actually started, child spans are still noop.
 noop3 := tr.StartSpan("noop3", opentracing.ChildOf(s1.Context()))
 if _, noop := noop3.(*noopSpan); !noop {
  t.Error("expected noop child span")
 }
 noop3.Finish()

 s1.LogKV("x", 1)
 StartRecording(s1, SingleNodeRecording)
 s1.LogKV("x", 2)
 s2 := tr.StartSpan("b", opentracing.ChildOf(s1.Context()))
 if IsBlackHoleSpan(s2) {
  t.Error("recording span should not be black hole")
 }
 s2.LogKV("x", 3)

 if err := TestingCheckRecordedSpans(GetRecording(s1), `
  span a:
   tags: unfinished=
   x: 2
  span b:
   tags: unfinished=
   x: 3
 `); err != nil {
  t.Fatal(err)
 }

 if err := TestingCheckRecordedSpans(GetRecording(s2), `
  span b:
   tags: unfinished=
   x: 3
 `); err != nil {
  t.Fatal(err)
 }

 s3 := tr.StartSpan("c", opentracing.FollowsFrom(s2.Context()))
 s3.LogKV("x", 4)
 s3.SetTag("tag", "val")

 s2.Finish()

 if err := TestingCheckRecordedSpans(GetRecording(s1), `
  span a:
   tags: unfinished=
   x: 2
  span b:
   x: 3
  span c:
   tags: tag=val unfinished=
   x: 4
 `); err != nil {
  t.Fatal(err)
 }
 s3.Finish()
 if err := TestingCheckRecordedSpans(GetRecording(s1), `
  span a:
      tags: unfinished=
   x: 2
  span b:
   x: 3
  span c:
   tags: tag=val
   x: 4
 `); err != nil {
  t.Fatal(err)
 }
 StopRecording(s1)
 s1.LogKV("x", 100)
 if err := TestingCheckRecordedSpans(GetRecording(s1), ``); err != nil {
  t.Fatal(err)
 }

 // The child span is still recording.
 s3.LogKV("x", 5)
 if err := TestingCheckRecordedSpans(GetRecording(s3), `
  span c:
   tags: tag=val
   x: 4
   x: 5
 `); err != nil {
  t.Fatal(err)
 }
 s1.Finish()
}

3.2 创建 childSpan 测试

测试 StartChildSpan，根据已有 span 创建出一个新的 span，为已有 span 的子 span。

func TestStartChildSpan(t *testing.T) {
 tr := NewTracer()
 sp1 := tr.StartSpan("parent", Recordable)
 StartRecording(sp1, SingleNodeRecording)
 sp2 := StartChildSpan("child", sp1, nil /* logTags */, false /*separateRecording*/)
 sp2.Finish()
 sp1.Finish()
 if err := TestingCheckRecordedSpans(GetRecording(sp1), `
  span parent:
   span child:
 `); err != nil {
  t.Fatal(err)
 }

 sp1 = tr.StartSpan("parent", Recordable)
 StartRecording(sp1, SingleNodeRecording)
 sp2 = StartChildSpan("child", sp1, nil /* logTags */, true /*separateRecording*/)
 sp2.Finish()
 sp1.Finish()
 if err := TestingCheckRecordedSpans(GetRecording(sp1), `
  span parent:
 `); err != nil {
  t.Fatal(err)
 }
 if err := TestingCheckRecordedSpans(GetRecording(sp2), `
  span child:
 `); err != nil {
  t.Fatal(err)
 }

 sp1 = tr.StartSpan("parent", Recordable)
 StartRecording(sp1, SingleNodeRecording)
 sp2 = StartChildSpan(
  "child", sp1, logtags.SingleTagBuffer("key", "val"), false, /*separateRecording*/
 )
 sp2.Finish()
 sp1.Finish()
 if err := TestingCheckRecordedSpans(GetRecording(sp1), `
  span parent:
   span child:
    tags: key=val
 `); err != nil {
  t.Fatal(err)
 }
}

3.3 跨进程追踪测试

测试跨进程追踪功能，主要是测试 inject 接口和 extract 接口，Inject 用于向 carrier 中注入 SpanContext 信息，Extract 用于从 carrier 中抽取出 SpanContext 信息。

 func TestTracerInjectExtract(t *testing.T) {
 tr := NewTracer()
 tr2 := NewTracer()

 // Verify that noop spans become noop spans on the remote side.

 noop1 := tr.StartSpan("noop")
 if _, noop := noop1.(*noopSpan); !noop {
  t.Fatalf("expected noop span: %+v", noop1)
 }
 carrier := make(opentracing.HTTPHeadersCarrier)
 if err := tr.Inject(noop1.Context(), opentracing.HTTPHeaders, carrier); err != nil {
  t.Fatal(err)
 }
 if len(carrier) != 0 {
  t.Errorf("noop span has carrier: %+v", carrier)
 }

 wireContext, err := tr2.Extract(opentracing.HTTPHeaders, carrier)
 if err != nil {
  t.Fatal(err)
 }
 if _, noopCtx := wireContext.(noopSpanContext); !noopCtx {
  t.Errorf("expected noop context: %v", wireContext)
 }
 noop2 := tr2.StartSpan("remote op", opentracing.FollowsFrom(wireContext))
 if _, noop := noop2.(*noopSpan); !noop {
  t.Fatalf("expected noop span: %+v", noop2)
 }
 noop1.Finish()
 noop2.Finish()

 // Verify that snowball tracing is propagated and triggers recording on the
 // remote side.

 s1 := tr.StartSpan("a", Recordable)
 StartRecording(s1, SnowballRecording)

 carrier = make(opentracing.HTTPHeadersCarrier)
 if err := tr.Inject(s1.Context(), opentracing.HTTPHeaders, carrier); err != nil {
  t.Fatal(err)
 }

 wireContext, err = tr2.Extract(opentracing.HTTPHeaders, carrier)
 if err != nil {
  t.Fatal(err)
 }
 s2 := tr2.StartSpan("remote op", opentracing.FollowsFrom(wireContext))

 // Compare TraceIDs
 trace1 := s1.Context().(*spanContext).TraceID
 trace2 := s2.Context().(*spanContext).TraceID
 if trace1 != trace2 {
  t.Errorf("TraceID doesn't match: parent %d child %d", trace1, trace2)
 }
 s2.LogKV("x", 1)
 s2.Finish()

 // Verify that recording was started automatically.
 rec := GetRecording(s2)
 if err := TestingCheckRecordedSpans(rec, `
  span remote op:
   tags: sb=1
   x: 1
 `); err != nil {
  t.Fatal(err)
 }

 if err := TestingCheckRecordedSpans(GetRecording(s1), `
  span a:
   tags: sb=1 unfinished=
 `); err != nil {
  t.Fatal(err)
 }

 if err := ImportRemoteSpans(s1, rec); err != nil {
  t.Fatal(err)
 }
 s1.Finish()

 if err := TestingCheckRecordedSpans(GetRecording(s1), `
  span a:
   tags: sb=1
  span remote op:
   tags: sb=1
   x: 1
 `); err != nil {
  t.Fatal(err)
 }
}

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