Add timeout check during Matches expression eval by jpbempel · Pull Request #12832 · DataDog/dd-trace-java

jpbempel · 2026-10-12T14:46:45Z

What Does This Do

In case of very expensive regex matching (like a backtracking one) timeout is not evaluated and only at the end of the evaluation. Using a CharSequence wrapper we can interleave a timeout check while accessing char through CharSequence::charAt(). regex expressions are also pre-compiled while before they was compiled
for each evaluation.

Motivation

Additional Notes

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Format the title according to the contribution guidelines
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Use solves instead, and assign the PR milestone to the issue
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Update public documentation with any new configuration flags or behaviors
Once approved, use merge queue to merge the PR

Jira ticket: DEBUG-6247

dd-octo-sts · 2026-10-12T14:46:59Z

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chatgpt-codex-connector · 2026-10-12T14:47:00Z

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📝 Code Review	✅ Completed 2026-10-12T14:51:25.091103Z	`7e7d696`	PR opened

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datadog-prod-us1-5

In CPU timeout mode, per-character CPU-time queries can make ordinary linear regex matches exhaust the 50 ms evaluation budget and suppress log-probe snapshots.

_{Open Bits AI session}

_{🤖 Bits Code Review · Commit 7e7d696}

dd-octo-sts · 2026-10-12T15:10:59Z

🟢 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	14.01 s	13.91 s	[-0.1%; +1.5%] (no difference)
startup:insecure-bank:tracing:Agent	12.87 s	12.99 s	[-1.5%; -0.3%] (maybe better)
startup:petclinic:appsec:Agent	17.22 s	17.09 s	[-0.0%; +1.5%] (no difference)
startup:petclinic:iast:Agent	16.89 s	17.01 s	[-1.5%; +0.1%] (no difference)
startup:petclinic:profiling:Agent	16.45 s	16.89 s	[-3.7%; -1.6%] (significantly better)
startup:petclinic:sca:Agent	17.08 s	17.09 s	[-1.0%; +0.8%] (no difference)
startup:petclinic:tracing:Agent	15.60 s	16.16 s	[-7.6%; +0.7%] (no difference)

Commit: 9572645e · 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.

pr-commenter · 2026-10-12T17:01:40Z

Debugger benchmarks

Parameters

	Baseline	Candidate
baseline_or_candidate	baseline	candidate
ci_job_date	1791961238	1791961565
end_time	2026-10-14T07:02:06	2026-10-14T07:07:33
git_branch	master	jpbempel/add-timeout-in-matches-expr
git_commit_sha	`0e86410`	`9572645`
start_time	2026-10-14T07:00:39	2026-10-14T07:06:06

See matching parameters

	Baseline	Candidate
ci_job_id	2136409532	2136409532
ci_pipeline_id	144523581	144523581
cpu_model	Intel(R) Xeon(R) Platinum 8259CL CPU @ 2.50GHz	Intel(R) Xeon(R) Platinum 8259CL CPU @ 2.50GHz
git_commit_date	1791960619	1791960619

Summary

Found 0 performance improvements and 0 performance regressions! Performance is the same for 9 metrics, 6 unstable metrics.

See unchanged results

scenario	Δ mean agg_http_req_duration_min	Δ mean agg_http_req_duration_p50	Δ mean agg_http_req_duration_p75	Δ mean agg_http_req_duration_p99	Δ mean throughput
scenario:noprobe	unstable [-41.032µs; +24.133µs] or [-12.625%; +7.426%]	unstable [-55.445µs; +34.925µs] or [-15.376%; +9.686%]	unstable [-67.606µs; +44.271µs] or [-17.944%; +11.750%]	unstable [-144982.888ns; +143774.194ns] or [-12.738%; +12.632%]	same
scenario:basic	same	same	same	unstable [-83.675µs; +162.394µs] or [-7.895%; +15.323%]	unstable [-165.371op/s; +165.371op/s] or [-7.276%; +7.276%]
scenario:loop	same	same	same	same	same

Request duration reports for reports

gantt
    title reports - request duration [CI 0.99] : candidate=None, baseline=None
    dateFormat X
    axisFormat %s
section baseline
noprobe (360.589 µs) : 312, 410
.   : milestone, 361,
basic (328.958 µs) : 323, 335
.   : milestone, 329,
loop (8.116 ms) : 8044, 8188
.   : milestone, 8116,
section candidate
noprobe (350.329 µs) : 314, 386
.   : milestone, 350,
basic (328.857 µs) : 323, 335
.   : milestone, 329,
loop (8.099 ms) : 8036, 8162
.   : milestone, 8099,

baseline results

Scenario	Request median duration [CI 0.99]
noprobe	360.589 µs [311.591 µs, 409.588 µs]
basic	328.958 µs [323.292 µs, 334.625 µs]
loop	8.116 ms [8.044 ms, 8.188 ms]

candidate results

Scenario	Request median duration [CI 0.99]
noprobe	350.329 µs [314.478 µs, 386.181 µs]
basic	328.857 µs [322.953 µs, 334.76 µs]
loop	8.099 ms [8.036 ms, 8.162 ms]

dudikeleti

LGTM, two nits:

If the regex fails to compile in the constructor, does that throw and fail the probe instead of returning an evaluation error?
Did you consider 1024 char check instead of 256?

jpbempel · 2026-10-13T12:50:42Z

LGTM, two nits:

If the regex fails to compile in the constructor, does that throw and fail the probe instead of returning an evaluation error?

it fails at deserialization from the json coming from RC so it will fail the whole probe definition back to RC. which makes sense here if the regex is not valid.

Did you consider 1024 char check instead of 256?

no, but testing around that, show me that I can push to 4096 to amortize the cost of the check

dd-octo-sts · 2026-10-13T14:39:58Z

/merge

gh-worker-devflow-routing-ef8351 · 2026-10-13T14:40:03Z

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2026-10-13 14:40:03 UTC ℹ️ Start processing command /merge

2026-10-13 14:40:07 UTC ℹ️ MergeQueue: pull request added to the queue

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

2026-10-13 15:26:51 UTC ❌ MergeQueue: The build pipeline contains failing jobs for this merge request

Build pipeline has failing jobs for 29189fa:

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Details

Since those jobs are not marked as being allowed to fail, the pipeline will most likely fail.
Therefore, and to allow other builds to be processed, this merge request has been rejected and the pipeline got canceled.

In case of very expensive regex matching (like a backtracking one) timeout is not evaluated and only at the end of the evaluation. Using a CharSequence wrapper we can interleave a timeout check while accessing char through CharSequence::charAt(). regex expression are also pre-compiled while before they was compiled for each evaluation.

dd-octo-sts · 2026-10-14T08:13:57Z

/merge

gh-worker-devflow-routing-ef8351 · 2026-10-14T08:14:04Z

View all feedbacks in Devflow UI.

2026-10-14 08:14:03 UTC ℹ️ Start processing command /merge

2026-10-14 08:14:09 UTC ℹ️ MergeQueue: pull request added to the queue

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

2026-10-14 09:25:32 UTC ℹ️ MergeQueue: This merge request was merged

jpbempel requested a review from a team as a code owner October 12, 2026 14:46

jpbempel requested review from dudikeleti and removed request for a team October 12, 2026 14:46

jpbempel added the comp: debugger Dynamic Instrumentation label Oct 12, 2026

jpbempel added the type: bug fix Bug fix label Oct 12, 2026

chatgpt-codex-connector Bot reviewed Oct 12, 2026

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Comment thread ...ebugger/debugger-el/src/main/java/com/datadog/debugger/el/expressions/MatchesExpression.java Outdated

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dudikeleti approved these changes Oct 13, 2026

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jpbempel added this pull request to the merge queue Oct 13, 2026

github-merge-queue Bot removed this pull request from the merge queue due to failed status checks Oct 13, 2026

jpbempel added 3 commits October 14, 2026 07:52

amortize timeout check

8b80baa

increase amortization to 4096

c8bc037

jpbempel force-pushed the jpbempel/add-timeout-in-matches-expr branch from e537d6e to c8bc037 Compare October 14, 2026 05:52

Fix equals hashCode for matches

9572645

jpbempel added this pull request to the merge queue Oct 14, 2026

github-merge-queue Bot removed this pull request from the merge queue due to failed status checks Oct 14, 2026

gh-worker-dd-mergequeue-cf854d Bot merged commit 5ea7911 into master Oct 14, 2026
618 checks passed

gh-worker-dd-mergequeue-cf854d Bot deleted the jpbempel/add-timeout-in-matches-expr branch October 14, 2026 09:25

github-actions Bot added this to the 1.68.0 milestone Oct 14, 2026

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