test(ddtrace/tracer): reproduce queue-full trace drops under a stalled agent by darccio · Pull Request #5140 · DataDog/dd-trace-go

darccio · 2026-08-05T14:36:51Z

Summary

Adds TestQueueOverflowOnStalledAgent, a deterministic testing/synctest-based harness that saturates the writer's concurrentConnectionLimit outgoing connections with a stalled agent stub (blockingTransport), forcing the tracer's single worker goroutine to block inside flush() and stop draining t.out.
Asserts payloadQueueSize overflows and the reason:queue_full counter (added in fix(ddtrace/tracer): instrument payload queue-full trace drops #5136) fires exactly once.

Part of #5135 (Part 4, item 1: "Reproduce the queue drop locally"). Stacked on #5136 — this PR's diff will shrink to just queue_overflow_test.go once that one merges.

Test plan

go build ./...
go vet ./...
go test . (full ddtrace/tracer package suite)
TestQueueOverflowOnStalledAgent run 20x with -race, no flakes
gofmt -l clean

…d agent Adds a deterministic synctest-based harness that saturates the writer's concurrentConnectionLimit outgoing connections with a stalled agent stub, forcing the single worker goroutine to block inside flush() and stop draining t.out. Asserts payloadQueueSize overflows and the reason:queue_full counter from #5136 fires exactly once. Part of #5135 (Part 4, item 1: reproduce the queue drop locally). Stacked on #5136.

github-actions · 2026-08-05T14:37:40Z

Config Audit

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datadog-prod-us1-5 · 2026-08-05T14:43:28Z

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 63.36% (-0.01%)

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: 6a80cda | Docs | Datadog PR Page | Give us feedback!}

pr-commenter · 2026-08-05T15:06:12Z

Benchmarks

Benchmark execution time: 2026-08-05 15:06:09

Comparing candidate commit 6a80cda in PR branch dario.castane/interesting-lichterman-535a86 with baseline commit 5a03f9a in branch dario.castane/wonderful-shirley-bc4283.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 326 metrics, 0 unstable metrics, 1 flaky benchmarks without significant changes.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

🟩 = significantly better candidate vs. baseline
🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

Known flaky benchmarks

These benchmarks are marked as flaky and will not trigger a failure. Modify FLAKY_BENCHMARKS_REGEX to control which benchmarks are marked as flaky.

Known flaky benchmarks without significant changes:

scenario:BenchmarkOTLPTraceWriterFlush

darccio requested a review from a team as a code owner August 5, 2026 14:36

darccio mentioned this pull request Aug 5, 2026

ddtrace/tracer: single-worker payload queue can silently drop traces (and waste already-spent CPU) under sustained load #5135

Open

kakkoyun approved these changes Aug 6, 2026

View reviewed changes

darccio added the AI Generated Largely based on code generated by an AI or LLM. This label is the same across all dd-trace-* repos label Aug 6, 2026

darccio merged commit 3905db8 into dario.castane/wonderful-shirley-bc4283 Aug 6, 2026
213 checks passed

darccio deleted the dario.castane/interesting-lichterman-535a86 branch August 6, 2026 14:37

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test(ddtrace/tracer): reproduce queue-full trace drops under a stalled agent - #5140

test(ddtrace/tracer): reproduce queue-full trace drops under a stalled agent#5140
darccio merged 1 commit into
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dario.castane/interesting-lichterman-535a86

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darccio commented Aug 5, 2026

Summary

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