Remove LegacyTagMap; OptimizedTagMap is the sole TagMap implementation by dougqh · Pull Request #11678 · DataDog/dd-trace-java

dougqh · 2026-06-18T17:35:03Z

What This Does

OptimizedTagMap has been the default for several months (the optimized.map.enabled flag defaulted to true). With Legacy effectively dead, this removes it so OptimizedTagMap is the sole TagMap implementor — satisfying CHA's unique-implementor precondition (a prerequisite for upcoming read-through / dense-store work).

Motivation

The removal of LegacyTagMap makes future changes to TagMap easier.
Possible future work includes...

deriving one TagMap from another TagMap
dense storage for known / commonly used tags

Changes

Delete LegacyTagMap and the whole TagMapFactory abstraction (the abstract class + its lone OptimizedTagMapFactory); TagMap.create()/create(int)/EMPTY now construct OptimizedTagMap directly.
Delete the now-trivial TagMapType / TagMapTypePair test enums and de-parameterize their tests to plain @Test. TagMapScenario (parameterizes by size) is kept.
Remove the optimized.map.enabled flag — Config field/getter, GeneralConfig constant, and the metadata/supported-configurations.json entry. Per the Config team, removing the registry entry is detected automatically at the next release (FPD + public docs get a Max Version: v1.xx.0 marker).

Notable

Fixes a latent static-init cycle that removing the flag exposed: TagMap (interface with default methods) ↔ OptimizedTagMap could leave TagMap.EMPTY null when OptimizedTagMap initialized first. A lazy EmptyHolder builds the empty singleton via the constructor instead of reading a mid-<clinit> static.
isOptimized() is intentionally left in place — it now constant-folds to true and is DCE'd at its call site (DDSpanContext); simplifying it away is a trivial follow-up.

Validation

internal-api TagMap suite green (TagMapTest, TagMapLedgerTest, TagMapFuzzTest); internal-api / dd-trace-api / dd-trace-core compile clean.
⏳ Draft pending a broader dd-trace-core integration run before marking ready.

Benchmark — overhead-neutral (parity)

TagMapAccessBenchmark (threading-correct, @Threads(8)) run on the pre-kill tree vs. this branch — the two differ by exactly these two commits (verified byte-identical pre-image). Throughput, 1 fork, 3 warmup + 5 measurement iters:

Benchmark	Pre-kill (ops/s)	Post-kill (ops/s)	Δ
`insert`	55.2M ±2.7M	53.9M ±6.2M	−2.3%
`getObject`	91.8M ±8.7M	93.3M ±10.2M	+1.6%
`getEntry`	91.7M ±18.2M	93.3M ±11.2M	+1.8%

All deltas are within run-to-run error (single fork) → no measurable change, as expected for a dead-code removal.

🤖 Generated with Claude Code

@test

With one implementor, the optimized/legacy split is dead weight. Delete LegacyTagMap and LegacyTagMapFactory; collapse the whole TagMapFactory abstraction (TagMap.create()/create(int)/EMPTY now construct OptimizedTagMap directly via a lazy EmptyHolder that avoids a TagMap<->OptimizedTagMap static-init cycle). OptimizedTagMap is the sole TagMap implementor, satisfying CHA's unique-implementor precondition. Delete the now-trivial TagMapType/TagMapTypePair test enums and de-parameterize their tests to plain @test; TagMapScenario (size-based) stays. Drop stale "legacy and optimized" references from javadoc. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

The flag only chose between the optimized and legacy TagMap impls; with Legacy gone it controls nothing. Remove the Config field/getter, the GeneralConfig constant, and the metadata/supported-configurations.json entry. Per the Config team, removing the registry entry is detected automatically at the next release (FPD + public docs get a "Max Version: v1.xx.0" marker), so the hard delete is the correct process. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dd-octo-sts · 2026-06-18T17:57:31Z

🟢 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	13.98 s	13.98 s	[-0.8%; +0.8%] (no difference)
startup:insecure-bank:tracing:Agent	12.89 s	12.94 s	[-1.0%; +0.2%] (no difference)
startup:petclinic:appsec:Agent	16.81 s	16.76 s	[-0.6%; +1.2%] (no difference)
startup:petclinic:iast:Agent	16.86 s	16.49 s	[-2.1%; +6.5%] (no difference)
startup:petclinic:profiling:Agent	16.81 s	16.69 s	[-0.5%; +2.1%] (no difference)
startup:petclinic:sca:Agent	16.55 s	16.67 s	[-5.1%; +3.7%] (no difference)
startup:petclinic:tracing:Agent	15.58 s	16.11 s	[-7.3%; +0.8%] (no difference)

Commit:a27e381b · 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.

bric3 · 2026-06-23T16:39:50Z

-/*
- * Using a class, so class hierarchy analysis kicks in
- * That will allow all of the calls to create methods to be devirtualized without a guard
- */


question: For my own information, do the hierarchy analysis do not work with interfaces ?

There are two flavors of hierarchy analysis.
There's single unique method which I believe does work for interfaces
-- and allows method call to be devirtualized
And there's single implementor which allows the reference to be refined to the more specific type
-- which in turn, then allows the method call to be devirtualized
And devirtualization can lead to inlining
There's also profile guided devirtualization which would work here, too, but that has a slightly higher execution cost

But then wouldn't that analysis also work if the factory was an interface ?
And there's single implementor which allows the reference to be refined to the more specific type
-- which in turn, then allows the method call to be devirtualized

bric3 · 2026-06-23T16:44:14Z

- "DD_OPTIMIZED_MAP_ENABLED": [
- {
- "version": "A",
- "type": "boolean",
- "default": "false",
- "aliases": []
- }
- ],


question: Might need some updated on the configuration portal

sarahchen6

Nice

Co-authored-by: Sarah Chen <sarah.chen@datadoghq.com>

mcculls

Nice, LGTM

dd-octo-sts · 2026-06-24T12:58:15Z

/merge

gh-worker-devflow-routing-ef8351 · 2026-06-24T12:58:19Z

View all feedbacks in Devflow UI.

2026-06-24 12:58:19 UTC ℹ️ Start processing command /merge

2026-06-24 12:58:24 UTC ℹ️ MergeQueue: pull request added to the queue

The expected merge time in master is approximately 1h (p90).

2026-06-24 14:06:20 UTC ℹ️ MergeQueue: This merge request was merged

dougqhand others added 2 commits June 18, 2026 13:32

dougqh added comp: core Tracer core tag: no release notes Changes to exclude from release notes type: refactoring tag: ai generated Largely based on code generated by an AI or LLM labels Jun 18, 2026

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dougqh mentioned this pull request Jun 18, 2026
Overhaul map JMH benchmarks: remove thread contention and split by use case #11679
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dougqh marked this pull request as ready for review June 23, 2026 14:55

dougqh requested review from a team as code owners June 23, 2026 14:55

dougqh requested review from mcculls and sarahchen6 and removed request for a teamJune 23, 2026 14:55

Merge branch 'master' into dougqh/kill-legacy-tagmap
ae106a7

bric3 approved these changes Jun 23, 2026
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sarahchen6 reviewed Jun 23, 2026
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Comment threadinternal-api/src/main/java/datadog/trace/api/TagMap.java Outdated

sarahchen6 approved these changes Jun 23, 2026
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Update internal-api/src/main/java/datadog/trace/api/TagMap.java
a27e381
Co-authored-by: Sarah Chen <sarah.chen@datadoghq.com>

mcculls approved these changes Jun 24, 2026
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dougqh added this pull request to the merge queue Jun 24, 2026

github-merge-queueBot removed this pull request from the merge queue due to failed status checks Jun 24, 2026

gh-worker-dd-mergequeue-cf854dBot merged commit c6f9664 into masterJun 24, 2026
583 checks passed

gh-worker-dd-mergequeue-cf854dBot deleted the dougqh/kill-legacy-tagmap branch June 24, 2026 14:06

github-actionsBot added this to the 1.64.0 milestone Jun 24, 2026

This was referenced Jun 29, 2026
Add missing coverage tests for OptimizedTagMap and EntryReadingHelper #11778
Merged
Store known span tags densely by tag-id in TagMap (concept draft) #11659
Closed

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Remove LegacyTagMap; OptimizedTagMap is the sole TagMap implementation - #11678

Remove LegacyTagMap; OptimizedTagMap is the sole TagMap implementation#11678
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What This Does

Motivation

Changes

Notable

Validation

Benchmark — overhead-neutral (parity)

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🟢 Java Benchmark SLOs — All performance SLOs passed

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