chore: improvements to ETP by hannahkm · Pull Request #4586 · DataDog/dd-trace-go

hannahkm · 2026-03-23T19:18:53Z

What does this PR do?

Set dummy values for when serialization fails to prevent failures during decoding
Removes duplicated serialization for span links

Motivation

Align with RFC and Java implementation.

Reviewer's Checklist

Changed code has unit tests for its functionality at or near 100% coverage.
System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
There is a benchmark for any new code, or changes to existing code.
If this interacts with the agent in a new way, a system test has been added.
New code is free of linting errors. You can check this by running make lint locally.
New code doesn't break existing tests. You can check this by running make test locally.
Add an appropriate team label so this PR gets put in the right place for the release notes.
All generated files are up to date. You can check this by running make generate locally.
Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild. Make sure all nested modules are up to date by running make fix-modules locally.

Unsure? Have a question? Request a review!

codecov · 2026-03-23T19:23:01Z

Codecov Report

❌ Patch coverage is 51.85185% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.74%. Comparing base (ee1fdc0) to head (7cf57c5).

Files with missing lines	Patch %	Lines
ddtrace/tracer/payload_v1.go	51.85%	13 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
ddtrace/tracer/payload_v1.go	`69.04% <51.85%> (ø)`

... and 375 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

datadog-datadog-prod-us1 · 2026-03-23T19:23:07Z

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 51.85%
• Overall Coverage: 60.07% (+4.07%)

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

🔗 Commit SHA: 7cf57c5 | Docs | Datadog PR Page | Was this helpful? React with 👍/👎 or give us feedback!}

pr-commenter · 2026-03-23T19:40:52Z

Benchmarks

Benchmark execution time: 2026-03-25 22:04:52

Comparing candidate commit 7cf57c5 in PR branch hannahkm/v1-followups with baseline commit ee1fdc0 in branch main.

Found 0 performance improvements and 13 performance regressions! Performance is the same for 202 metrics, 9 unstable metrics.

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 ----------------------------------'

scenario:BenchmarkPayloadVersions/detailed_1000spans/v1_0-25

🟥 allocated_mem [+5 bytes; +6 bytes] or [+5.228%; +5.588%]
🟥 execution_time [+39.931µs; +42.600µs] or [+6.705%; +7.153%]

scenario:BenchmarkPayloadVersions/detailed_100spans/v1_0-25

🟥 execution_time [+3.894µs; +4.153µs] or [+6.395%; +6.820%]

scenario:BenchmarkPayloadVersions/detailed_10spans/v1_0-25

🟥 execution_time [+380.690ns; +424.910ns] or [+5.170%; +5.770%]

scenario:BenchmarkPayloadVersions/detailed_1spans/v1_0-25

🟥 execution_time [+36.562ns; +50.638ns] or [+2.405%; +3.331%]

scenario:BenchmarkPayloadVersions/metastruct_1000spans/v1_0-25

🟥 execution_time [+23.781µs; +25.105µs] or [+7.259%; +7.664%]

scenario:BenchmarkPayloadVersions/metastruct_100spans/v1_0-25

🟥 execution_time [+2.503µs; +2.711µs] or [+6.612%; +7.161%]

scenario:BenchmarkPayloadVersions/metastruct_10spans/v1_0-25

🟥 execution_time [+232.414ns; +310.986ns] or [+3.301%; +4.417%]

scenario:BenchmarkPayloadVersions/simple_1000spans/v1_0-25

🟥 allocated_mem [+3 bytes; +3 bytes] or [+6.502%; +7.647%]
🟥 execution_time [+24.314µs; +25.155µs] or [+8.596%; +8.893%]

scenario:BenchmarkPayloadVersions/simple_100spans/v1_0-25

🟥 execution_time [+2.425µs; +2.538µs] or [+8.247%; +8.630%]

scenario:BenchmarkPayloadVersions/simple_10spans/v1_0-25

🟥 execution_time [+247.027ns; +277.373ns] or [+6.271%; +7.042%]

scenario:BenchmarkPayloadVersions/simple_1spans/v1_0-25

🟥 execution_time [+44.503ns; +65.697ns] or [+4.017%; +5.930%]

darccio · 2026-03-26T08:22:02Z

@codex review

chatgpt-codex-connector · 2026-03-26T08:26:46Z

Codex Review: Didn't find any major issues. Nice work!

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darccio

In general it's fine, but the regressions must be addressed.

I'm curious why we need to set _dd.span_links when we could just postpone the serialization until the very moment we really need to.

darccio · 2026-03-26T15:23:13Z

ddtrace/tracer/payload_v1.go

+		log.Warn("failed to serialize unsupported fieldValue type for field %d", fieldID)
+		buf = st.serialize(serializationFailed, buf)


These lines increases encodeField inlining cost, altering how this function can inline too its own callees.

$ go build -gcflags="-m=2" ./ddtrace/tracer/ | grep encodeField # main: encodeField[go.shape.string]: cost 667 exceeds budget 80 # PR: encodeField[go.shape.string]: cost 801 exceeds budget 80

We can reduce the inlining cost by wrapping log.Warn in a go:noinline-tagged function:

//go:noinline func warnUnsupportedFieldValue(fieldID uint32) { log.Warn("failed to serialize unsupported fieldValue type for field %d", fieldID) }

darccio · 2026-03-26T15:23:38Z

ddtrace/tracer/payload_v1.go

+		_, containsSpanLinks := span.meta["_dd.span_links"]
+		if containsSpanLinks {
+			size--
+		}


This causes part of the execution time regressions. This can be changed to:

Suggested change

}

size := len(span.metrics) + len(span.metaStruct)

for k := range span.meta {

if k != "_dd.span_links" {

size++

}

}

hannahkm added 3 commits March 23, 2026 09:21

wip: default value for failed serialization

db1fbc2

write dummy value as a byte for meta_struct

44211b7

dont double encode span links on spans

f3ac9a2

hannahkm added 4 commits March 24, 2026 10:24

fix: reduce heap allocs?

fef304e

trigger tests

5a8e764

lint: don't use %v

f81c6ec

fix: array length with _dd.span_links was wrong

ec8baf2

hannahkm marked this pull request as ready for review March 25, 2026 21:32

hannahkm requested a review from a team as a code owner March 25, 2026 21:32

Merge branch 'main' into hannahkm/v1-followups

7cf57c5

darccio requested changes Mar 26, 2026

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chore: improvements to ETP#4586

chore: improvements to ETP#4586
hannahkm wants to merge 8 commits intomainfrom
hannahkm/v1-followups

hannahkm commented Mar 23, 2026 •

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		log.Warn("failed to serialize unsupported fieldValue type for field %d", fieldID)
		buf = st.serialize(serializationFailed, buf)

-		}
+		size := len(span.metrics) + len(span.metaStruct)
+		for k := range span.meta {
+			if k != "_dd.span_links" {
+				size++
+			}
+		}

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What does this PR do?

Motivation

Reviewer's Checklist

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Benchmarks

Explanation

More details about the CI and significant changes

scenario:BenchmarkPayloadVersions/detailed_1000spans/v1_0-25

scenario:BenchmarkPayloadVersions/detailed_100spans/v1_0-25

scenario:BenchmarkPayloadVersions/detailed_10spans/v1_0-25

scenario:BenchmarkPayloadVersions/detailed_1spans/v1_0-25

scenario:BenchmarkPayloadVersions/metastruct_1000spans/v1_0-25

scenario:BenchmarkPayloadVersions/metastruct_100spans/v1_0-25

scenario:BenchmarkPayloadVersions/metastruct_10spans/v1_0-25

scenario:BenchmarkPayloadVersions/simple_1000spans/v1_0-25

scenario:BenchmarkPayloadVersions/simple_100spans/v1_0-25

scenario:BenchmarkPayloadVersions/simple_10spans/v1_0-25

scenario:BenchmarkPayloadVersions/simple_1spans/v1_0-25

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hannahkm commented Mar 23, 2026 •

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