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Fixes issue 27567 - tail_sampling processor metrics wrong #27568

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Fixes issue 27567 - tail_sampling processor metrics wrong #27568

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27 changes: 27 additions & 0 deletions .chloggen/27567-tailsampler-fix-metrics.yaml
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Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
# Use this changelog template to create an entry for release notes.

# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
change_type: 'bug_fix'

# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
component: processor/tailsamplingprocessor

# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
note: Publish tail_sampler count_traces_sampled metric differently per individual policy

# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
issues: [27567]

# (Optional) One or more lines of additional information to render under the primary note.
# These lines will be padded with 2 spaces and then inserted directly into the document.
# Use pipe (|) for multiline entries.
subtext: Fixes tail_sampler count_traces_sampled metric to report sampled true/false count per policy. Previously all policies received the same count based on the sampling "final decision"

# If your change doesn't affect end users or the exported elements of any package,
# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
# Optional: The change log or logs in which this entry should be included.
# e.g. '[user]' or '[user, api]'
# Include 'user' if the change is relevant to end users.
# Include 'api' if there is a change to a library API.
# Default: '[user]'
change_logs: [user]
31 changes: 18 additions & 13 deletions processor/tailsamplingprocessor/processor.go
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ import (
"fmt"
"math"
"runtime"
"strconv"
"sync"
"sync/atomic"
"time"
Expand Down Expand Up @@ -252,18 +253,22 @@ func (tsp *tailSamplingSpanProcessor) makeDecision(id pcommon.TraceID, trace *sa
switch decision {
case sampling.Sampled:
samplingDecision[sampling.Sampled] = true
tsp.recordPolicySampledDecisionMetric(p, true)
trace.Decisions[i] = decision

case sampling.NotSampled:
samplingDecision[sampling.NotSampled] = true
tsp.recordPolicySampledDecisionMetric(p, false)
trace.Decisions[i] = decision

case sampling.InvertSampled:
samplingDecision[sampling.InvertSampled] = true
tsp.recordPolicySampledDecisionMetric(p, true)
trace.Decisions[i] = sampling.Sampled

case sampling.InvertNotSampled:
samplingDecision[sampling.InvertNotSampled] = true
tsp.recordPolicySampledDecisionMetric(p, false)
trace.Decisions[i] = sampling.NotSampled
}
}
Expand All @@ -279,28 +284,17 @@ func (tsp *tailSamplingSpanProcessor) makeDecision(id pcommon.TraceID, trace *sa
finalDecision = sampling.Sampled
}

for i, p := range tsp.policies {
switch trace.Decisions[i] {
for _, p := range tsp.policies {
switch finalDecision {
case sampling.Sampled:
// any single policy that decides to sample will cause the decision to be sampled
// the nextConsumer will get the context from the first matching policy
if matchingPolicy == nil {
matchingPolicy = p
}

_ = stats.RecordWithTags(
p.ctx,
[]tag.Mutator{tag.Upsert(tagSampledKey, "true")},
statCountTracesSampled.M(int64(1)),
)
metrics.decisionSampled++

case sampling.NotSampled:
_ = stats.RecordWithTags(
p.ctx,
[]tag.Mutator{tag.Upsert(tagSampledKey, "false")},
statCountTracesSampled.M(int64(1)),
)
metrics.decisionNotSampled++
}
}
Expand All @@ -323,6 +317,17 @@ func (tsp *tailSamplingSpanProcessor) makeDecision(id pcommon.TraceID, trace *sa
return finalDecision, matchingPolicy
}

func (tsp *tailSamplingSpanProcessor) recordPolicySampledDecisionMetric(policy *policy, sampled bool) {
_ = stats.RecordWithTags(
policy.ctx,
[]tag.Mutator{
tag.Upsert(tagPolicyKey, policy.name),
tag.Upsert(tagSampledKey, strconv.FormatBool(sampled)),
},
statCountTracesSampled.M(int64(1)),
)
}

// ConsumeTraces is required by the processor.Traces interface.
func (tsp *tailSamplingSpanProcessor) ConsumeTraces(_ context.Context, td ptrace.Traces) error {
resourceSpans := td.ResourceSpans()
Expand Down