consumer: improve performance of EventsGroup

[wk989898]

What problem does this PR solve?

Issue Number: close #5937

What is changed and how it works?

• AppendMessage records whether the message is out of order or not, with the overhead of comparing neighboring CommitTs just once.
• In normal order, ResolveInto uses sort. Search to find message boundaries with CommitTs <= resolveTs directly, instead of traversing all the search, instead of traversing all messages at once and allocating temporary resolved slices.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

  Scenario, 16K messages	Before	After	Improvement
  No messages resolved	139.9 µs/op	14.6 ns/op	roughly 9,500×
  Half resolved	161.4 µs/op	7.16 µs/op	roughly 22.5×
  All resolved	175.6 µs/op	8.06 µs/op	roughly 21.8×

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

• Performance

  • Improved event resolution when messages arrive out of timestamp order.
  • Optimized processing of buffered events, including partial and complete resolution scenarios.

• Tests

  • Added benchmark coverage for ordered, out-of-order, partial, and full event resolution across large message sets.

[coderabbitai]

📝 Walkthrough

Walkthrough

EventsGroup now tracks out-of-order message insertion, sorts buffered messages when needed, and resolves messages through binary search and in-place removal. A benchmark measures ordered and out-of-order resolution across partial and complete workloads.

Changes

Event resolution

Layer / File(s)	Summary
Out-of-order tracking and prefix resolution cmd/util/event_group.go	EventsGroup detects timestamp disorder. ResolveInto sorts when required, finds the resolvable prefix with binary search, logs the count, resets ordering state, and removes messages in place.
Resolution benchmark coverage cmd/util/event_group_test.go	A benchmark measures ordered and out-of-order resolution for no-op, partial, and full cases across 16K messages while reusing buffers and suppressing logging.

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

Poem

I’m a rabbit sorting timestamps bright,
Finding the prefix just right.
Buffers stay swift,
Resolved rows lift,
And benchmarks measure the flight.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Linked Issues check	❓ Inconclusive	The changes improve EventsGroup resolution, but the provided context does not show that they restore CREATE DATABASE synchronization for Kafka changefeeds [#5937].	Add a regression test or other evidence that confirms CREATE DATABASE events synchronize correctly under the issue's Kafka configuration.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Out of Scope Changes check	✅ Passed	The code and benchmark changes concern EventsGroup resolution and performance, with no clearly unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title clearly identifies the main change: improving EventsGroup performance in the consumer.
Description check	✅ Passed	The description includes the issue, implementation summary, test coverage, and benchmark results, but leaves the questions and release note sections incomplete.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[wk989898]

/test all

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 3AceShowHand, asddongmen

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Details

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• OWNERS [3AceShowHand,asddongmen]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-08-10 10:27:34.588932255 +0000 UTC m=+3042240.625027311: ☑️ agreed by 3AceShowHand.
• 2026-08-11 05:14:43.901564927 +0000 UTC m=+3109869.937659973: ☑️ agreed by asddongmen.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #5948.