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Always record force keep decisions for future distributed trace propagation #10308

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Merged
mcculls merged 1 commit into from
Jan 7, 2026
Merged

Always record force keep decisions for future distributed trace propagation #10308

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7 changes: 3 additions & 4 deletions dd-trace-core/src/main/java/datadog/trace/core/DDSpanContext.java
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Original file line number Diff line number Diff line change
Expand Up @@ -530,10 +530,9 @@ public void forceKeep(byte samplingMechanism) {
private void forceKeepThisSpan(byte samplingMechanism) {
// if the user really wants to keep this trace chunk, we will let them,
// even if the old sampling priority and mechanism have already propagated
if (SAMPLING_PRIORITY_UPDATER.getAndSet(this, PrioritySampling.USER_KEEP)
== PrioritySampling.UNSET) {
propagationTags.updateTraceSamplingPriority(PrioritySampling.USER_KEEP, samplingMechanism);
}
SAMPLING_PRIORITY_UPDATER.set(this, PrioritySampling.USER_KEEP);
// record force keep decision for future distributed trace propagation
propagationTags.forceKeep(samplingMechanism);
}

public void addPropagatedTraceSource(final int value) {
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2 changes: 2 additions & 0 deletions dd-trace-core/src/main/java/datadog/trace/core/propagation/PropagationTags.java
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Expand Up @@ -57,6 +57,8 @@ public interface Factory {
*/
public abstract void updateTraceSamplingPriority(int samplingPriority, int samplingMechanism);

public abstract void forceKeep(int samplingMechanism);

public abstract int getSamplingPriority();

public abstract void updateTraceOrigin(CharSequence origin);
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59 changes: 34 additions & 25 deletions dd-trace-core/src/main/java/datadog/trace/core/propagation/ptags/PTagsFactory.java
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Expand Up @@ -185,37 +185,46 @@ static PTags withError(PTagsFactory factory, String error) {
public void updateTraceSamplingPriority(int samplingPriority, int samplingMechanism) {
if (samplingPriority != PrioritySampling.UNSET && canChangeDecisionMaker
|| samplingMechanism == SamplingMechanism.EXTERNAL_OVERRIDE) {
if (this.samplingPriority != samplingPriority) {
// This should invalidate any cached w3c header
clearCachedHeader(W3C);
doUpdateTraceSamplingPriority(samplingPriority, samplingMechanism);
}
}

@Override
public void forceKeep(int samplingMechanism) {
doUpdateTraceSamplingPriority(PrioritySampling.USER_KEEP, samplingMechanism);
}

private void doUpdateTraceSamplingPriority(int samplingPriority, int samplingMechanism) {
if (this.samplingPriority != samplingPriority) {
// This should invalidate any cached w3c header
clearCachedHeader(W3C);
}
this.samplingPriority = samplingPriority;
if (samplingPriority > 0) {
// TODO should try to keep the old sampling mechanism if we override the value?
if (samplingMechanism == SamplingMechanism.EXTERNAL_OVERRIDE) {
// There is no specific value for the EXTERNAL_OVERRIDE, so say that it's the DEFAULT
samplingMechanism = SamplingMechanism.DEFAULT;
}
this.samplingPriority = samplingPriority;
if (samplingPriority > 0) {
// TODO should try to keep the old sampling mechanism if we override the value?
if (samplingMechanism == SamplingMechanism.EXTERNAL_OVERRIDE) {
// There is no specific value for the EXTERNAL_OVERRIDE, so say that it's the DEFAULT
samplingMechanism = SamplingMechanism.DEFAULT;
}
// Protect against possible SamplingMechanism.UNKNOWN (-1) that doesn't comply with the
// format
if (samplingMechanism >= 0) {
TagValue newDM = TagValue.from("-" + samplingMechanism);
if (!newDM.equals(decisionMakerTagValue)) {
// This should invalidate any cached w3c and datadog header
clearCachedHeader(DATADOG);
clearCachedHeader(W3C);
}
decisionMakerTagValue = newDM;
}
} else {
// Drop the decision maker tag
if (decisionMakerTagValue != null) {
// Protect against possible SamplingMechanism.UNKNOWN (-1) that doesn't comply with the
// format
if (samplingMechanism >= 0) {
TagValue newDM = TagValue.from("-" + samplingMechanism);
if (!newDM.equals(decisionMakerTagValue)) {
// This should invalidate any cached w3c and datadog header
clearCachedHeader(DATADOG);
clearCachedHeader(W3C);
}
decisionMakerTagValue = null;
decisionMakerTagValue = newDM;
}
} else {
// Drop the decision maker tag
if (decisionMakerTagValue != null) {
// This should invalidate any cached w3c and datadog header
clearCachedHeader(DATADOG);
clearCachedHeader(W3C);
}
decisionMakerTagValue = null;
}
}

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18 changes: 8 additions & 10 deletions dd-trace-core/src/test/groovy/datadog/trace/core/DDSpanContextPropagationTagsTest.groovy
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Expand Up @@ -99,11 +99,10 @@ class DDSpanContextPropagationTagsTest extends DDCoreSpecification {
dd.createTagMap() == tagMap

where:
priority | header | newHeader | tagMap
UNSET | "_dd.p.usr=123" | "_dd.p.dm=-4,_dd.p.usr=123" | ["_dd.p.dm": "-4", "_dd.p.usr": "123"]
// decision has already been made, propagate as-is
SAMPLER_KEEP | "_dd.p.dm=9bf3439f2f-1,_dd.p.usr=123" | "_dd.p.dm=9bf3439f2f-1,_dd.p.usr=123" | ["_dd.p.dm": "9bf3439f2f-1", "_dd.p.usr": "123"]
SAMPLER_KEEP | "_dd.p.usr=123" | "_dd.p.usr=123" | ["_dd.p.usr": "123"]
priority | header | newHeader | tagMap
UNSET | "_dd.p.usr=123" | "_dd.p.dm=-4,_dd.p.usr=123" | ["_dd.p.dm": "-4", "_dd.p.usr": "123"]
SAMPLER_KEEP | "_dd.p.dm=9bf3439f2f-1,_dd.p.usr=123" | "_dd.p.dm=-4,_dd.p.usr=123" | ["_dd.p.dm": "-4", "_dd.p.usr": "123"]
SAMPLER_KEEP | "_dd.p.usr=123" | "_dd.p.dm=-4,_dd.p.usr=123" | ["_dd.p.dm": "-4", "_dd.p.usr": "123"]
}

def "forceKeep trace PropagationTags #priority #header"() {
Expand All @@ -127,10 +126,9 @@ class DDSpanContextPropagationTagsTest extends DDCoreSpecification {
ddRoot.createTagMap() == rootTagMap

where:
priority | header | rootHeader | rootTagMap
UNSET | "_dd.p.usr=123" | "_dd.p.dm=-4,_dd.p.usr=123" | ["_dd.p.dm": "-4", "_dd.p.usr": "123"]
// decision has already been made, propagate as-is
SAMPLER_KEEP | "_dd.p.dm=9bf3439f2f-1,_dd.p.usr=123" | "_dd.p.dm=9bf3439f2f-1,_dd.p.usr=123" | ["_dd.p.dm": "9bf3439f2f-1", "_dd.p.usr": "123"]
SAMPLER_KEEP | "_dd.p.usr=123" | "_dd.p.usr=123" | ["_dd.p.usr": "123"]
priority | header | rootHeader | rootTagMap
UNSET | "_dd.p.usr=123" | "_dd.p.dm=-4,_dd.p.usr=123" | ["_dd.p.dm": "-4", "_dd.p.usr": "123"]
SAMPLER_KEEP | "_dd.p.dm=9bf3439f2f-1,_dd.p.usr=123" | "_dd.p.dm=-4,_dd.p.usr=123" | ["_dd.p.dm": "-4", "_dd.p.usr": "123"]
SAMPLER_KEEP | "_dd.p.usr=123" | "_dd.p.dm=-4,_dd.p.usr=123" | ["_dd.p.dm": "-4", "_dd.p.usr": "123"]
}
}