按照【云溪数据库 Tracing（一）】介绍的使用 opentracing 要求，本文着重介绍云溪数据库 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
在云溪数据库中的实现
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 - 云溪数据库中
Opentracing 简单使用示例
3.1 开启 Tracer Recording 测试
云溪数据库中 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)
}
}