When Span and Trace IDs match inconsistent results are returned

[joe-elliott]

Describe the bug
I'm unsure what the "correct" behavior is here, but if a trace and span id collide Tempo will return one span or the other based on the order that the spans are fed into CombineTraces.

This is slightly more likely to occur then it sounds. The way that the Jaeger go client samples traces can increase the chance of collisions:

jaegertracing/jaeger-client-go#582

And the same client uses the trace id for its root span guaranteeing a span id collision if the trace ids collide:

https://github.com/jaegertracing/jaeger-client-go/blob/master/tracer.go#L278

The end result is that Tempo non-deterministically returns one root span or the other (along with the rest of the traces) due to the behavior of:

tempo/pkg/model/combine.go

Line 22 in c1b49d7

func (o objectCombiner) Combine(objA []byte, objB []byte, dataEncoding string) ([]byte, bool) {

[github-actions]

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