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ddtrace/tracer: Always count dropped p0 traces and spans #1461

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merged 3 commits into from
Sep 9, 2022
Merged

ddtrace/tracer: Always count dropped p0 traces and spans #1461

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d751c06
ddtrace/tracer: Always count dropped p0 traces and spans
ajgajg1134 Sep 9, 2022
7543cf0
Have to update version
ajgajg1134 Sep 9, 2022
42b5cba
Refactor to reduce duplication / make logic more clear, Thanks Katie
ajgajg1134 Sep 9, 2022
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2 changes: 2 additions & 0 deletions ddtrace/tracer/tracer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -335,6 +335,8 @@ func (t *tracer) sampleFinishedTrace(info *finishedTrace) {
return
}
if !t.rulesSampling.HasSpanRules() {
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I played around with this a bit just to understand the logic better. What do you think about something like this? Do you find it more readable / less error-prone?

func (t *tracer) sampleFinishedTrace(info *finishedTrace) {
	if info.decision == decisionKeep {
		return
	}
	var kept []*span
	if t.rulesSampling.HasSpanRules() {
		// Apply sampling rules to individual spans in the trace.
		for _, span := range info.spans {
			if t.rulesSampling.SampleSpan(span) {
				kept = append(kept, span)
			}
		}
		if len(kept) > 0 && len(kept) < len(info.spans) {
			// Some spans in the trace were kept, so a partial trace will be sent.
			atomic.AddUint64(&t.partialTraces, 1)
		}
	}
	if len(kept) == 0 {
		atomic.AddUint64(&t.droppedP0Traces, 1)
	}
	atomic.AddUint64(&t.droppedP0Spans, uint64(len(info.spans)-len(kept)))
	info.spans = kept
}

I also think there might be a bug. atomic.AddUint64(&t.partialTraces, 1) will be called today if len(kept) == 0, but isn't it possible that every span is kept, s.t. we keep the entire trace, even when applying the single span sampling rules? In that case, we aren't sending a partial trace, but a whole trace.

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Hmm that's a good point. I'm not sure if all the spans arriving to the backend but as "single span ingested" affects the way they're displayed or how hit metrics are calculated such that even though all the spans arrived it's not really a trace since they're marked specially as "single span ingested"?

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I'm not sure either. If you want to just remove that && len(kept) < len(info.spans) for now and re-introduce it later after we've looked at it we can. But I assume for this patch it doesn't make a difference since no one is using single span rules today anyway.

atomic.AddUint64(&t.droppedP0Traces, 1)
atomic.AddUint64(&t.droppedP0Spans, uint64(len(info.spans)))
info.spans = nil
return
}
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5 changes: 5 additions & 0 deletions ddtrace/tracer/tracer_test.go
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Expand Up @@ -351,6 +351,11 @@ func TestSamplingDecision(t *testing.T) {

t.Run("client_dropped", func(t *testing.T) {
tracer, _, _, stop := startTestTracer(t)
defer func() {
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We should do these same checks for the single spans code too. Since no one is using it, it's fine if we do that in a follow-up PR though.

// Must check these after tracer is stopped to avoid flakiness
assert.Equal(t, uint64(1), tracer.droppedP0Traces)
assert.Equal(t, uint64(2), tracer.droppedP0Spans)
}()
defer stop()
tracer.config.agent.DropP0s = true
tracer.config.sampler = NewRateSampler(0)
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2 changes: 1 addition & 1 deletion internal/version/version.go
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Expand Up @@ -8,4 +8,4 @@ package version
// Tag specifies the current release tag. It needs to be manually
// updated. A test checks that the value of Tag never points to a
// git tag that is older than HEAD.
const Tag = "v1.41.0"
const Tag = "v1.41.1"