code: func StartSaveSpan(ctx context.Context) context.Context {
  	if !Enabled {
  		return ctx
  	}
  	traceId := ctx.Value(StoreLabelId)
  
  	if traceId != nil {
  		traceStr := traceId.(string)
  		var sp opentracing.Span
  		ctx, sp = spancontext.StartSpan(
  			ctx,
  			traceStr,
  		)
  		traceMeta := ctx.Value(StoreLabelMeta)
  		if traceMeta != nil {
  			traceStr = traceStr + "." + traceMeta.(string)
  		}
  		store.spans.Store(traceStr, sp)
  	}
  	return ctx
  }
docs: // StartSaveSpan stores the span specified in the passed context for later retrieval
  // The span object but be context value on the key StoreLabelId.
  // It will be stored under the the following string key context.Value(StoreLabelId)|.|context.Value(StoreLabelMeta)