[demo] Add Bucket4j rate-limiter instrumentation by dougqh · Pull Request #11903 · DataDog/dd-trace-java

dougqh · 2026-07-09T19:22:08Z

⚠️Demo artifact — do not merge. Will be closed after the talk.

This PR exists to demo the AI-assisted performance-review rubric for the Java build-team talk. The instrumentation is intentionally written with several hot-path anti-patterns in Bucket4jDecorator.onConsume (which runs on every Bucket#tryConsume):

per-call InstrumenterConfig.get().isIntegrationEnabled(singleton(...)) — config lookup + a fresh set allocation every call
Arrays.stream(...).filter(...).findFirst() in the hot path
Objects.hash(...) — varargs array + boxing every call
eager LOGGER.debug("..." + ... + bucket) string building

…alongside a benign one-time use of the sameObjects.hash pattern in cold static init (buildKnownLimitKeys).

The point of the demo: the reviewer should flag the hot-path costs and stay silent on the cold one — situational awareness, not a linter.

🤖 Generated with Claude Code

Traces bucket4j rate-limit checks: one span per Bucket#tryConsume with tokens/consumed tags and a rate tier. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dd-octo-sts · 2026-07-09T20:11:06Z

🟢 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	14.77 s	14.66 s	[-0.1%; +1.6%] (no difference)
startup:insecure-bank:tracing:Agent	13.60 s	13.70 s	[-1.5%; -0.1%] (maybe better)
startup:petclinic:appsec:Agent	16.79 s	16.80 s	[-1.1%; +0.9%] (no difference)
startup:petclinic:iast:Agent	16.86 s	16.92 s	[-1.4%; +0.6%] (no difference)
startup:petclinic:profiling:Agent	16.40 s	16.88 s	[-7.2%; +1.5%] (no difference)
startup:petclinic:sca:Agent	16.94 s	16.82 s	[+0.1%; +1.4%] (maybe worse)
startup:petclinic:tracing:Agent	16.14 s	16.21 s	[-1.3%; +0.5%] (no difference)

Commit:62abebcb · 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.

dougqh

From Claude perf rubric...

Perf review (rubric: `perf-review-checks.md`)

Scope: Bucket4jDecorator.onConsume — runs on every Bucket#tryConsume call (tracing hot path; multiplier = per-call × calls/sec).

Confirmed findings

1. Per-call config lookup + Set allocation

InstrumenterConfig.get().isIntegrationEnabled(singleton("bucket4j-tier"), true)

Collections.singleton(...) allocates a new SingletonSet every call, plus a config lookup, for a value that doesn't change per-call.

Rubric check #2 (repeat work on invariant input) — SEV-2/3
Fix: hoist to a static final boolean (or cache in a field) computed once.

2. Arrays.stream(...).filter(...).findFirst() in the hot path
Builds a Stream pipeline (Stream + Spliterator + pipeline stages + captured lambda) every call just to find the first threshold ≥ tokens.

Rubric check #1/#5 (per-call allocation + unnecessary indirection) — SEV-3
Fix: plain for loop over TIER_THRESHOLDS, no Stream.

3. Objects.hash(bucket, tokens, consumed) in onConsume
Varargs Object[] allocation + boxing of tokens (long) and consumed (boolean) on every call, unconditionally.

Rubric check J9 — SEV-2/3
Fix: datadog.trace.util.HashingUtils (no boxing, no array).

4. Eager string concatenation in LOGGER.debug(...)

LOGGER.debug("bucket4j tryConsume tokens=" + tokens + " consumed=" + consumed + " bucket=" + bucket);

Builds the string unconditionally, even when debug logging is disabled.

Rubric check #2/J10 — SEV-2/3
Fix: SLF4J parameterized form, or guard with isDebugEnabled().

Correctly not flagged

DEFAULT_LIMIT_KEY = Objects.hash("default", 100L) — same Objects.hash pattern as #3, but this one runs once at class-init (cold path). Per the rubric's precision-over-recall posture, staying silent here.

Posted per the AI-review rubric demo — no action required for this closed/demo PR.

dougqh

Perf review per perf-review-checks.md rubric — 4 hot-path findings inline below. onConsume runs on every Bucket#tryConsume call, so multiplier = per-call × calls/sec.

dougqh · 2026-07-09T20:45:31Z

+
+ public void onConsume(AgentSpan span, Bucket bucket, long tokens, boolean consumed) {
+ long tier = -1L;
+ if (InstrumenterConfig.get().isIntegrationEnabled(singleton("bucket4j-tier"), true)) {


Per-call config lookup + Set allocation.Collections.singleton("bucket4j-tier") allocates a new SingletonSet every call, plus a config lookup, for a value that doesn't change per-call.
Rubric check First PR - Implements the Opentracing API #2 (repeat work on invariant input) — SEV-2/3
Fix: hoist to a static final boolean (or cache in a field) computed once.

dougqh · 2026-07-09T20:45:31Z

+ long tier = -1L;
+ if (InstrumenterConfig.get().isIntegrationEnabled(singleton("bucket4j-tier"), true)) {
+ tier =
+ Arrays.stream(TIER_THRESHOLDS)


Stream pipeline in the hot path.Arrays.stream(...).filter(...).findFirst() builds a Stream + Spliterator + pipeline stages + captured lambda every call just to find the first threshold ≥ tokens.
Rubric check changing List<Span> for List<DDSpan> #1/Gpolaert/dev #5 (per-call allocation + unnecessary indirection) — SEV-3
Fix: plain for loop over TIER_THRESHOLDS, no Stream.

dougqh · 2026-07-09T20:45:31Z

+ span.setTag("bucket4j.tier", tier);
+ }
+
+ int metricKey = Objects.hash(bucket, tokens, consumed);


Objects.hash varargs/boxing on the hot path.Objects.hash(bucket, tokens, consumed) allocates an Object[] and boxes tokens/consumed on every call, unconditionally.
Rubric check J9 — SEV-2/3
Fix: datadog.trace.util.HashingUtils (no boxing, no array).
(Not flagging DEFAULT_LIMIT_KEY = Objects.hash("default", 100L) above at line 27 — that one runs once at class-init, cold path.)

dougqh · 2026-07-09T20:45:31Z

+ }
+
+ LOGGER.debug(
+ "bucket4j tryConsume tokens=" + tokens + " consumed=" + consumed + " bucket=" + bucket);


Eager string concatenation in LOGGER.debug(...). The string is built unconditionally (StringBuilder + bucket.toString()), even when debug logging is disabled.
Rubric check First PR - Implements the Opentracing API #2/J10 — SEV-2/3
Fix: SLF4J parameterized form LOGGER.debug("bucket4j tryConsume tokens={} consumed={} bucket={}", tokens, consumed, bucket), or guard with isDebugEnabled().

dougqh · 2026-07-09T22:52:47Z

+ private static final long[] TIER_THRESHOLDS = {1L, 10L, 100L, 1_000L, 10_000L};
+
+ // stable id for the default bandwidth profile; computed once at class load
+ private static final int DEFAULT_LIMIT_KEY = Objects.hash("default", 100L);


Objects.hash called - but only once during class initialization, so not alerted.

dougqh · 2026-07-13T17:22:21Z

This just intended as a test / demo of the perf review skill. It has fulfilled that purpose.

dougqhand others added 2 commits July 9, 2026 14:45

Add Bucket4j (tryConsume) instrumentation
ebd6032
Traces bucket4j rate-limit checks: one span per Bucket#tryConsume with tokens/consumed tags and a rate tier. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Simplify bucket4j limit-key handling
62abebc
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dougqh commented Jul 9, 2026
View reviewed changes

dougqh closed this Jul 13, 2026

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[demo] Add Bucket4j rate-limiter instrumentation - #11903

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🟢 Java Benchmark SLOs — All performance SLOs passed

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Perf review (rubric: perf-review-checks.md)

Confirmed findings

Correctly not flagged

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