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Fix: preserve delta start timestamp in fast path #4069

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Fix: preserve delta start timestamp in fast path #4069

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c6738ce
fix: preserve delta start timestamp in fast path
fmutlu68 May 8, 2026
7e4e191
Merge branch 'main' into fix-delta-start-ts
ThomsonTan May 11, 2026
39f0888
Add delta counter empty-cycle timestamp test
fmutlu68 May 11, 2026
c4c0e1f
fix: update start timestamp for empty cycles in delta metrics
fmutlu68 May 12, 2026
cf0cc76
chore: fix formatting errors
fmutlu68 May 12, 2026
06e92a4
chore: fix format errors, last one
fmutlu68 May 12, 2026
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2 changes: 2 additions & 0 deletions sdk/include/opentelemetry/sdk/metrics/state/temporal_metric_storage.h
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,8 @@ class TemporalMetricStorage
// Lock while building metrics
mutable opentelemetry::common::SpinLockMutex lock_;
const AggregationConfig *aggregation_config_;
opentelemetry::common::SystemTimestamp last_delta_collection_ts_;
bool has_last_delta_collection_ts_ = false;
};
} // namespace metrics
} // namespace sdk
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8 changes: 7 additions & 1 deletion sdk/src/metrics/state/temporal_metric_storage.cc
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Expand Up @@ -54,6 +54,11 @@ bool TemporalMetricStorage::buildMetrics(CollectorHandle *collector,
// no other reader configured to collect those data.
if (collectors.size() == 1 && aggregation_temporarily == AggregationTemporality::kDelta)
{
if (!has_last_delta_collection_ts_)
{
last_delta_collection_ts_ = sdk_start_ts;
has_last_delta_collection_ts_ = true;
}
// If no metrics, early return
if (delta_metrics->Size() == 0)
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@ThomsonTan ThomsonTan May 11, 2026

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On the empty-collection path, the function early-returns when delta_metrics->Size() == 0 before updating last_delta_collection_ts_. If a cycle at t2 is empty and the next cycle at t3 has data, the emitted point will carry start_ts = t1 (the last non-empty collection) rather than t2, even though the delta map only contains activity from (t2, t3]. Successive delta windows then overlap instead of abutting, which violates the OTel data model's requirement that start_ts(n) == end_ts(n-1) and causes rate computations (value / (end - start)) to under-report. The slow path doesn't have this issue because last_reported_metrics_[collector].collection_ts is updated on every call, including empty ones.

{
Expand All @@ -63,8 +68,9 @@ bool TemporalMetricStorage::buildMetrics(CollectorHandle *collector,
MetricData metric_data;
metric_data.instrument_descriptor = instrument_descriptor_;
metric_data.aggregation_temporality = AggregationTemporality::kDelta;
metric_data.start_ts = sdk_start_ts;
metric_data.start_ts = last_delta_collection_ts_;
metric_data.end_ts = collection_ts;
last_delta_collection_ts_ = collection_ts;

// Direct conversion of delta metrics to point data
delta_metrics->GetAllEntries(
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