fix(ddtrace/tracer): pre-compute `_dd.p.dm` numeric value at write-time by darccio · Pull Request #4576 · DataDog/dd-trace-go

darccio · 2026-03-20T15:36:35Z

What does this PR do?

Moves the strconv.ParseInt call for _dd.p.dm (decision maker) out of the v1 payload flush path and into the write path.

A dm uint32 field is added to the trace struct. It is kept in sync with propagatingTags[keyDecisionMaker] at all mutation sites (setPropagatingTagLocked, unsetPropagatingTagLocked, replacePropagatingTags). A shared unsetPropagatingTagLocked helper is introduced so the delete-and-clear logic is not duplicated between unsetPropagatingTag and setSamplingPriorityLockedWithForce.

payloadV1.push now reads the pre-computed value via trace.decisionMaker() instead of fetching the string from the propagating tags map and parsing it on every flush.

Motivation

payloadV1.push is called once per finished trace chunk. On every call it was acquiring a read lock, doing a map lookup, and then running strconv.ParseInt — all to read a value that was set at most once or twice during the lifetime of the trace. Moving the parse to write-time eliminates the per-flush map lookup and parse, replacing them with a single scalar read behind an RLock.

Reviewer's Checklist

Changed code has unit tests for its functionality at or near 100% coverage.
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.

codecov · 2026-03-20T15:41:56Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.63%. Comparing base (0472a95) to head (1be56bb).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
ddtrace/tracer/payload_v1.go	`68.55% <100.00%> (ø)`
ddtrace/tracer/propagating_tags.go	`78.57% <100.00%> (ø)`
ddtrace/tracer/spancontext.go	`92.65% <100.00%> (ø)`

... and 437 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 · 2026-03-20T15:41:58Z

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 59.90% (+0.09%)

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

🔗 Commit SHA: 1be56bb | Docs | Datadog PR Page | Was this helpful? React with 👍/👎 or give us feedback!}

pr-commenter · 2026-03-24T07:49:42Z

Benchmarks

Benchmark execution time: 2026-03-25 09:38:05

Comparing candidate commit 1be56bb in PR branch dario.castane/langplat-59/no-parseint-on-dm with baseline commit 0472a95 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 215 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 ----------------------------------'

kakkoyun

LGTM

…` in the conditional body Co-authored-by: Benjamin De Bernardi <[email protected]>

…com:Datadog/dd-trace-go into dario.castane/langplat-59/no-parseint-on-dm

darccio · 2026-03-24T18:18:21Z

@codex review

chatgpt-codex-connector

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: f6898ef772

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

Open a pull request for review
Mark a draft as ready
Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

chatgpt-codex-connector · 2026-03-24T18:22:10Z

-				log.Error("failed to convert decision maker to uint32: %s", err.Error())
-			}
-		}
+		sm = span.context.trace.decisionMaker()


Preserve _dd.p.dm when encoding chunks from generic contexts

payloadV1.push now reads only trace.decisionMaker(), but the cache is not initialized on every path that sets propagating tags. In particular, FromGenericCtx assigns sc.trace.propagatingTags = ctx.PropagatingTags() directly (without calling setPropagatingTagLocked/replacePropagatingTags), so traces built from generic contexts that carry _dd.p.dm will emit samplingMechanism=0 instead of the propagated value. Before this commit, push parsed _dd.p.dm from the tags map at flush time, so this is a behavior regression for that integration path.

Useful? React with 👍 / 👎.

…eneric span contexts

…com:Datadog/dd-trace-go into dario.castane/langplat-59/no-parseint-on-dm

darccio · 2026-03-25T09:09:15Z

/merge

gh-worker-devflow-routing-ef8351 · 2026-03-25T09:09:20Z

View all feedbacks in Devflow UI.

2026-03-25 09:09:19 UTC ℹ️ Start processing command /merge

2026-03-25 09:09:26 UTC ℹ️ MergeQueue: waiting for PR to be ready

This pull request is not mergeable according to GitHub. Common reasons include pending required checks, missing approvals, or merge conflicts — but it could also be blocked by other repository rules or settings.
It will be added to the queue as soon as checks pass and/or get approvals. View in MergeQueue UI.
Note: if you pushed new commits since the last approval, you may need additional approval.
You can remove it from the waiting list with /remove command.

2026-03-25 09:41:10 UTC ℹ️ MergeQueue: merge request added to the queue

The expected merge time in main is approximately 29m (p90).

2026-03-25 09:54:45 UTC ℹ️ MergeQueue: This merge request was merged

…me (#4576) ### What does this PR do? Moves the `strconv.ParseInt` call for `_dd.p.dm` (decision maker) out of the v1 payload flush path and into the write path. A `dm uint32` field is added to the `trace` struct. It is kept in sync with `propagatingTags[keyDecisionMaker]` at all mutation sites (`setPropagatingTagLocked`, `unsetPropagatingTagLocked`, `replacePropagatingTags`). A shared `unsetPropagatingTagLocked` helper is introduced so the delete-and-clear logic is not duplicated between `unsetPropagatingTag` and `setSamplingPriorityLockedWithForce`. `payloadV1.push` now reads the pre-computed value via `trace.decisionMaker()` instead of fetching the string from the propagating tags map and parsing it on every flush. ### Motivation `payloadV1.push` is called once per finished trace chunk. On every call it was acquiring a read lock, doing a map lookup, and then running `strconv.ParseInt` — all to read a value that was set at most once or twice during the lifetime of the trace. Moving the parse to write-time eliminates the per-flush map lookup and parse, replacing them with a single scalar read behind an `RLock`. ### Reviewer's Checklist - [x] Changed code has unit tests for its functionality at or near 100% coverage. - [x] New code is free of linting errors. You can check this by running `make lint` locally. - [x] New code doesn't break existing tests. You can check this by running `make test` locally. - [x] Add an appropriate team label so this PR gets put in the right place for the release notes. - [x] All generated files are up to date. You can check this by running `make generate` locally. Co-authored-by: dario.castane <[email protected]>

fix(ddtrace/tracer): pre-compute _dd.p.dm numeric value at write-time

7fb5b34

Merge branch 'main' into dario.castane/langplat-59/no-parseint-on-dm

c5801c6

darccio marked this pull request as ready for review March 24, 2026 08:26

darccio requested review from a team as code owners March 24, 2026 08:26

kakkoyun approved these changes Mar 24, 2026

View reviewed changes

genesor approved these changes Mar 24, 2026

View reviewed changes

Comment thread ddtrace/tracer/propagating_tags.go Outdated

Comment thread ddtrace/tracer/propagating_tags.go

darccio and others added 4 commits March 24, 2026 12:23

fix(ddtrace/tracer): isolate specific behaviour for `keyDecisionMaker…

78cb149

…` in the conditional body Co-authored-by: Benjamin De Bernardi <[email protected]>

feat(ddtrace/tracer): reintroduce logging on decision maker parsing

603b407

Merge branch 'dario.castane/langplat-59/no-parseint-on-dm' of github.…

fd17e64

…com:Datadog/dd-trace-go into dario.castane/langplat-59/no-parseint-on-dm

Merge branch 'main' into dario.castane/langplat-59/no-parseint-on-dm

f6898ef

chatgpt-codex-connector Bot reviewed Mar 24, 2026

View reviewed changes

darccio added 2 commits March 24, 2026 18:26

fix(ddtrace/tracer): ensure that decisionMaker is updated even from g…

a4807f5

…eneric span contexts

Merge branch 'dario.castane/langplat-59/no-parseint-on-dm' of github.…

64e6faf

…com:Datadog/dd-trace-go into dario.castane/langplat-59/no-parseint-on-dm

gh-worker-dd-devflow-36fce6 Bot added mergequeue-status: waiting mergequeue-status: removed and removed mergequeue-status: waiting labels Mar 24, 2026

darccio added 2 commits March 25, 2026 08:58

chore(ddtrace/tracer): make format

89cbca4

chore(ddtrace/tracer): checklocks

1be56bb

darccio force-pushed the dario.castane/langplat-59/no-parseint-on-dm branch from 2a2cae7 to 1be56bb Compare March 25, 2026 09:08

gh-worker-dd-devflow-36fce6 Bot added mergequeue-status: waiting mergequeue-status: queued and removed mergequeue-status: removed mergequeue-status: waiting labels Mar 25, 2026

gh-worker-dd-devflow-36fce6 Bot added mergequeue-status: in_progress and removed mergequeue-status: queued labels Mar 25, 2026

gh-worker-dd-mergequeue-cf854d Bot merged commit ef7877e into main Mar 25, 2026
209 checks passed

gh-worker-dd-devflow-36fce6 Bot removed the mergequeue-status: in_progress label Mar 25, 2026

gh-worker-dd-mergequeue-cf854d Bot deleted the dario.castane/langplat-59/no-parseint-on-dm branch March 25, 2026 09:54

gh-worker-dd-devflow-36fce6 Bot added the mergequeue-status: done label Mar 25, 2026

darccio mentioned this pull request Apr 20, 2026

feat(ddtrace/tracer): add span lifecycle benchmarks #4682

Merged

7 tasks

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

fix(ddtrace/tracer): pre-compute `_dd.p.dm` numeric value at write-time#4576

fix(ddtrace/tracer): pre-compute `_dd.p.dm` numeric value at write-time#4576
gh-worker-dd-mergequeue-cf854d[bot] merged 10 commits into
mainfrom
dario.castane/langplat-59/no-parseint-on-dm

darccio commented Mar 20, 2026 •

edited

Loading

Uh oh!

codecov Bot commented Mar 20, 2026 •

edited

Loading

Uh oh!

datadog-datadog-prod-us1 Bot commented Mar 20, 2026 •

edited by datadog-official Bot

Loading

Uh oh!

pr-commenter Bot commented Mar 24, 2026 •

edited

Loading

Explanation

More details about the CI and significant changes

Uh oh!

kakkoyun left a comment

Uh oh!

Uh oh!

Uh oh!

darccio commented Mar 24, 2026

Uh oh!

chatgpt-codex-connector Bot left a comment

Uh oh!

chatgpt-codex-connector Bot Mar 24, 2026

Uh oh!

darccio commented Mar 25, 2026

Uh oh!

gh-worker-devflow-routing-ef8351 Bot commented Mar 25, 2026 •

edited

Loading

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Uh oh!

Conversation

darccio commented Mar 20, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

What does this PR do?

Motivation

Reviewer's Checklist

Uh oh!

codecov Bot commented Mar 20, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

datadog-datadog-prod-us1 Bot commented Mar 20, 2026 • edited by datadog-official Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

pr-commenter Bot commented Mar 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Benchmarks

Explanation

More details about the CI and significant changes

Uh oh!

kakkoyun left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

darccio commented Mar 24, 2026

Uh oh!

chatgpt-codex-connector Bot left a comment

Choose a reason for hiding this comment

💡 Codex Review

Uh oh!

chatgpt-codex-connector Bot Mar 24, 2026

Choose a reason for hiding this comment

Uh oh!

darccio commented Mar 25, 2026

Uh oh!

gh-worker-devflow-routing-ef8351 Bot commented Mar 25, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

darccio commented Mar 20, 2026 •

edited

Loading

codecov Bot commented Mar 20, 2026 •

edited

Loading

datadog-datadog-prod-us1 Bot commented Mar 20, 2026 •

edited by datadog-official Bot

Loading

pr-commenter Bot commented Mar 24, 2026 •

edited

Loading

gh-worker-devflow-routing-ef8351 Bot commented Mar 25, 2026 •

edited

Loading