eventbroker: fix broker quota release and message validation

[lidezhu]

What problem does this PR solve?

Issue Number: close #5642

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Please refer to [Release Notes Language Style Guide](https://pingcap.github.io/tidb-dev-guide/contribute-to-tidb/release-notes-style-guide.html) to write a quality release note.

If you don't think this PR needs a release note then fill it with `None`.

Summary by CodeRabbit

• Bug Fixes

  • Fixed changefeed scan quota handling so allocated capacity is properly returned after scan failures, interruptions, and partial scans.
  • Prevented invalid heartbeat and congestion-control messages from causing processing errors.
  • Corrected dispatcher metrics to include table-trigger dispatchers.

• Tests

  • Added coverage for quota recovery, scan errors, invalid messages, and dispatcher metric tracking.

[ti-chi-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[coderabbitai]

📝 Walkthrough

Walkthrough

Eventservice scan quota cleanup now covers early exits and scan failures, table-trigger dispatcher metrics remain balanced, and malformed heartbeat or congestion-control messages are ignored safely after logging.

Changes

Eventservice corrections

Layer / File(s)	Summary
Scan quota release and failure coverage pkg/eventservice/event_broker.go, pkg/eventservice/event_broker_test.go, pkg/eventservice/test_helper.go	doScan releases allocated quota on insufficient quota, scan errors, invalid scans, and partial scans. Tests cover quota restoration and injected table-info failures.
Table-trigger dispatcher gauge accounting pkg/eventservice/event_broker.go, pkg/eventservice/event_broker_test.go	Table-trigger dispatcher registration increments the dispatcher gauge, and tests verify the gauge returns to baseline after removal.
Invalid message payload handling pkg/eventservice/event_service.go, pkg/eventservice/event_service_test.go	Heartbeat and congestion-control messages with invalid payload lengths return early, with tests covering nil payloads.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Suggested labels: lgtm, approved

Suggested reviewers: asddongmen, wk989898, flowbehappy

Poem

I’m a rabbit with quotas tucked neat,
No leaked bytes beneath my feet.
Gauges hop in balanced rows,
Bad messages meet quick “no.”
Tests cheer: “The burrow’s bright!” 🐇

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description includes the issue number, but the required change summary, tests, questions, and release note are left empty or generic.	Fill in what changed, list the tests run, answer the compatibility/documentation questions, and replace the release-note placeholder with a real note or None.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR addresses all three linked objectives: quota release, dispatcher gauge balance, and safe invalid-message handling.
Out of Scope Changes check	✅ Passed	The added tests and mock support are directly tied to the stated fixes and no unrelated code changes stand out.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title matches the main fixes: broker quota release and message validation.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ldz/fix-event-broker0712

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[gemini-code-assist]

Code Review

This pull request introduces fixes to the event service, including releasing memory quota when skipping scans due to insufficient quota, tracking table trigger dispatchers in metrics, and handling invalid message payloads by returning early. Corresponding unit tests have been added. The review feedback points out a potential quota leak if scanning fails later in the process, and warns about unsafe type assertions on message payloads that could lead to panics, suggesting safer 'comma-ok' type assertions instead.

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[gemini-code-assist]

While releasing the allocated quota here is necessary, a similar quota leak can occur if scanner.scan fails further down in this function (around line 728). When scanner.scan returns an error, the remaining scannedBytes of the allocated quota is not fully released, which can lead to temporary quota exhaustion until the next congestion control update.

Consider fully releasing the remaining quota in the error handling block of scanner.scan as well:

if err != nil {
    if scannedBytes > 0 {
        releaseQuota(available, uint64(min(sl.maxDMLBytes, scannedBytes)))
    }
    log.Error("scan events failed", ...)
    return
}

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: asddongmen, hongyunyan

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• OWNERS [asddongmen,hongyunyan]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-07-13 03:29:38.662831394 +0000 UTC m=+597964.698926440: ☑️ agreed by hongyunyan.
• 2026-07-13 09:08:49.884144872 +0000 UTC m=+618315.920239918: ☑️ agreed by asddongmen.

[ti-chi-bot]

@lidezhu: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-unit-test	47a25dc	link	unknown	/test pull-unit-test
pull-unit-test-next-gen	47a25dc	link	unknown	/test pull-unit-test-next-gen

Full PR test history. Your PR dashboard.

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