Pre-construct TagMap.Entry objects in InternalTagsAdder by dougqh · Pull Request #11555 · DataDog/dd-trace-java

dougqh · 2026-06-04T00:12:48Z

What Does This Do

InternalTagsAdder sets _dd.base_service / version on spans via TagMap.set(tag, value), which allocates a fresh TagMap.Entryper span. Both values are fixed for the life of the tracer, and TagMap.Entry objects are explicitly safe to share across maps (the OptimizedTagMap collision design via BucketGroup relies on it). This pre-builds the two Entry objects once in the constructor and reuses them via set(entry).

Motivation

A JFR allocation profile of spring-petclinic under load (full agent, 2026-06-03) attributed ~52 allocation samples to InternalTagsAdder.processTags — one Entry allocated per span for base.service. Tag-map handling (TagMap$Entry + OptimizedTagMap) was the single largest non-core tracer allocation theme in that profile, ahead of the CSS metrics system. This change drops the InternalTagsAdder contribution to zero.

Notes

Re-applies the logic from Reuse TagMap.Entry objects in InternalTagsAdder #10965 (dd/pre-construct-tagmap-entries), which had drifted 415 commits behind master and changed processTags's signature; this version sits on current master with the unchanged AppendableSpanLinks signature. Supersedes Reuse TagMap.Entry objects in InternalTagsAdder #10965.
Behavior preserved: Entry.stringValue() for the OBJECT entry resolves to obj.toString() (cached), identical to the prior ddService.toString() in the equalsIgnoreCase comparison. The only edge case — empty ddService now yields an early return — is unreachable in production (Config.getServiceName() is never "").
Existing test InternalTagsAdderTest.groovy passes unchanged.

🤖 Generated with Claude Code

InternalTagsAdder set base.service / version via TagMap.set(tag, value), allocating a fresh TagMap.Entry per span. Both values are fixed for the life of the tracer, and TagMap.Entry objects are safe to share across maps (the OptimizedTagMap collision design relies on it), so build the two Entry objects once in the constructor and reuse them via set(entry). A JFR profile of petclinic (2026-06-03) attributed ~52 allocation samples to InternalTagsAdder.processTags (one Entry per span); this drops them to zero. Re-applies the change from the stale PR #10965 (415 commits behind master, drifted signature) onto current master. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

dd-octo-sts · 2026-06-04T00:14:16Z

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Addresses the Codex review comment on #11555: pre-building the base.service Entry must not change behavior for an explicitly-empty DD_SERVICE. Entry.create rejects empty values, so baseServiceEntry is null in that case; the processTags branch now falls back to set(BASE_SERVICE, ddService) to preserve byte-identical behavior, and the version branch is still reached when the span service also matches the empty configured service. Migrate InternalTagsAdderTest from Groovy/Spock to JUnit 5 (parameterized with @MethodSource) and add regression coverage for the empty-DD_SERVICE case (9 migrated cases + 2 new = 11). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

dd-octo-sts · 2026-06-04T01:38:31Z

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	13.97 s	13.93 s	[-0.5%; +1.1%] (no difference)
startup:insecure-bank:tracing:Agent	12.86 s	12.99 s	[-1.6%; -0.3%] (maybe better)
startup:petclinic:appsec:Agent	16.94 s	16.74 s	[+0.3%; +2.0%] (maybe worse)
startup:petclinic:iast:Agent	17.00 s	17.02 s	[-0.9%; +0.6%] (no difference)
startup:petclinic:profiling:Agent	16.68 s	17.03 s	[-3.3%; -0.8%] (maybe better)
startup:petclinic:sca:Agent	16.80 s	16.70 s	[-0.3%; +1.5%] (no difference)
startup:petclinic:tracing:Agent	15.68 s	15.98 s	[-6.0%; +2.3%] (no difference)

Commit:6b1a26f9 · CI Pipeline · Benchmarking Platform UI

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

amarziali

it looks a good idea. I left improvements for the comments specifically that looks a bit too verbosely generated

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

@TableTest

…gression test Preserves the @TableTest versions of the two existing tests that landed on master, and adds the empty-DD_SERVICE regression test (from the PR) as a plain @test. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

- Extend the processTags null guard to also exit when ddService.length()==0, which prevents writing _dd.base_service="" via the TagMap.set path that has no empty-value guard (unlike Entry.create). Empty ddService now behaves the same as null/unset. - Remove the manual null+length>0 pre-check before TagMap.Entry.create in the constructor; Entry.create already returns null for null or empty values, so the guard was redundant. - Update the regression test to assert the new early-return behavior. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Handle the per-span "common" tags (base.service / version) via the tag-id fast path. These values are fixed for the tracer's life, so build their TagMap.Entry once and share across every span (Entry is immutable + safe to share) — dropping InternalTagsAdder's per-span Entry allocation to zero (cf. PR #11555, the string-keyed precursor), and making the entries tag-id-bearing so they also land in their positional slot. - TagMap.Entry.create(long, Object)/create(long, CharSequence): tag-id keyed, null/empty-rejecting factories mirroring the String create(). - CoreTagIds.BASE_SERVICE / VERSION (stored range) + resolver entries. - InternalTagsAdder prebuilds baseServiceEntry/versionEntry in its ctor and set()s the shared entry; empty DD_SERVICE early-returns (regression test added). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

amarziali · 2026-06-10T06:58:51Z

 public void processTags(
 TagMap unsafeTags, DDSpanContext spanContext, AppendableSpanLinks spanLinks) {
- if (spanContext == null || ddService == null) {
+ if (spanContext == null || ddService == null || ddService.length() == 0) {


when that processor is created (in createEagerChain) the ddService value is taken from Config.getServiceName() and this cannot be neither null neither empty. So it looks that instead adding a check for the size we can also remove the null check. I would suggest to improve the documentation (i.e. also add @NonNull to the constructor and simplify that instructions

This was primarily out of an abundance of caution. Although, both AI and human reviewers had raised this as potential concern, so it was easiest to just be cautious.
If you are confident that empty won't reach here, then we can change it.

From Claude...
Good call — confirmed that createEagerChain() always passes Config.getServiceName() which defaults to "unnamed-java-app" and is never null or empty. Changed the constructor param to @Nonnull, dropped the null check on ddService, and simplified the guard in processTags to just spanContext == null.

amarziali · 2026-06-10T07:03:22Z

+ // Regression: empty DD_SERVICE is treated the same as unset — processTags exits early and
+ // writes no tags, regardless of the span's service name.
+ @Test
+ void emptyDdServiceWritesNoTags() {


This test should not be added. I don't understand why the regression word is used here. And the service name cannot be empty in our tracer. I would suggest to remove it and improve the documentation of this processor as suggested above

It is a change in behavior of the InternalTagsAdder, so this test was guarding against that change/regression being introduced again. Mostly, it just comes down to the contract being unclear before, so the AI had to be cautious.

From Claude...
Agreed — removed the test and the @Test import. The contract is now documented by the @Nonnull annotation on the constructor instead.

@empty

…ession test Config.getServiceName() always returns a non-null non-empty string (defaults to "unnamed-java-app"), so the null/@empty guard in processTags and the corresponding regression test for empty DD_SERVICE are unnecessary. Replaced @nullable with @nonnull on the constructor param to document the actual contract. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dd-octo-sts · 2026-06-22T22:55:42Z

/merge

gh-worker-devflow-routing-ef8351 · 2026-06-22T22:55:46Z

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2026-06-22 22:55:46 UTC ℹ️ Start processing command /merge

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2026-06-23 00:35:32 UTC ℹ️ MergeQueue: This merge request was merged

dougqh mentioned this pull request Jun 4, 2026
Reuse TagMap.Entry objects in InternalTagsAdder #10965
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dougqh marked this pull request as ready for review June 4, 2026 00:14

dougqh requested a review from a team as a code owner June 4, 2026 00:14

dougqh requested a review from ygree June 4, 2026 00:14

dd-octo-stsBot added the tag: ai generated Largely based on code generated by an AI or LLM label Jun 4, 2026

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Comment threaddd-trace-core/src/main/java/datadog/trace/core/tagprocessor/InternalTagsAdder.java Outdated

dougqh added comp: core Tracer core type: feature Enhancements and improvements tag: performance Performance related changes labels Jun 4, 2026

amarziali reviewed Jun 8, 2026
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dougqhand others added 4 commits June 9, 2026 13:02

Trim verbose generated comments in InternalTagsAdder per review feedback
c773ba7
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Merge branch 'master' into dougqh/preconstruct-internal-tags
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bric3 approved these changes Jun 15, 2026
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Merge branch 'master' into dougqh/preconstruct-internal-tags
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sarahchen6 approved these changes Jun 22, 2026
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dougqh added this pull request to the merge queue Jun 22, 2026

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gh-worker-dd-mergequeue-cf854dBot merged commit e3a0877 into masterJun 23, 2026
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gh-worker-dd-mergequeue-cf854dBot deleted the dougqh/preconstruct-internal-tags branch June 23, 2026 00:35

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bric3 mentioned this pull request Jul 15, 2026
InternalTagAdder: defensively guard against null prebuilt tagmap entry #11958
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