mysql: move MySQL-only metrics into the MySQL sink package

[3AceShowHand]

What problem does this PR solve?

Issue Number: close #5867

Metrics that only apply to the MySQL sink were defined and registered in pkg/metrics. Affected-row recording and cleanup were also part of the generic metrics.Statistics type, although the values come from sql.Result.RowsAffected() in the MySQL writer. This split ownership across the generic metrics package and the MySQL sink.

What is changed and how it works?

• Move the affected-row, transaction worker, conflict detection, and active-active conflict collectors to pkg/sink/mysql/metrics.go.
• Record affected-row metrics in mysql.Writer and cache each labeled counter handle so WithLabelValues is called only on the first use.
• Remove MySQL-specific affected-row state and methods from metrics.Statistics.
• Register MySQL sink collectors through mysql.InitMetrics.
• Reuse metrics.GetKeyspaceLabel for legacy and next-generation label names.
• Delete affected-row series for a changefeed when its MySQL sink closes.
• Fix encoder group metrics collection and cleanup: sample all input and output channel sizes with one ticker, populate the previously unused output-channel gauge, and delete the labeled series when the group exits.

The Prometheus metric names, labels, help text, and histogram buckets are unchanged. The encoder group output-channel gauge is now populated as intended.

Check List

Tests

• Unit test
• Integration test
• Manual test
• No code

The following checks passed:

• go test ./pkg/sink/mysql -run "^TestDMLEventRowsAffectedMetrics$" -count=1
• go test --tags=intest ./pkg/sink/mysql -run "^TestDMLEventRowsAffectedMetrics$" -count=1
• go test ./pkg/metrics -count=1
• go test ./downstreamadapter/sink/mysql/causality ./downstreamadapter/sink/mysql ./server -run "^$" -count=1

Questions

Will it cause performance regression or break compatibility?

No performance regression is expected. The MySQL writer caches labeled affected-row counters instead of calling WithLabelValues for every DML event.

The Prometheus contract is unchanged. The Go collector variables move from pkg/metrics to pkg/sink/mysql, and all in-repository callers are updated.

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

No. Existing dashboards and Prometheus queries continue to use the same metric names and labels.

Release note

None

Summary by CodeRabbit

• New Features

  • Added detailed MySQL sink metrics for DML row counts, conflict handling, and worker performance.
  • Added encoder queue-depth monitoring across input and output channels.
  • Improved cleanup of per-changefeed and per-input metrics.

• Bug Fixes

  • Corrected metric registration and labeling to improve monitoring consistency.
  • Prevented stale metrics from remaining after changefeeds or encoder inputs are removed.

• Refactor

  • Consolidated metric ownership under the relevant MySQL sink and encoder components.
  • Removed obsolete transaction and row-tracking metrics.

[coderabbitai]

📝 Walkthrough

Walkthrough

The change exports the keyspace label helper, moves MySQL-specific Prometheus metrics into pkg/sink/mysql, updates metric recording and cleanup, removes generic row-affected tracking, and centralizes encoder queue metric collection.

Changes

Metrics Ownership Migration

Layer / File(s)	Summary
Export shared keyspace label helper pkg/metrics/*.go	GetKeyspaceLabel() replaces the private helper across shared metric definitions.
Add MySQL metric package pkg/sink/mysql/metrics.go, pkg/sink/mysql/metrics_test.go, server/metrics.go	The MySQL sink defines and registers DML, conflict, and worker metrics. Tests cover affected-row recording and per-changefeed deletion.
Wire MySQL metric recording pkg/sink/mysql/mysql_writer.go, pkg/sink/mysql/mysql_writer_dml_exec.go, pkg/sink/mysql/mysql_writer_for_active_active_sync_stats.go, downstreamadapter/sink/mysql/causality/conflict_detector.go, downstreamadapter/sink/mysql/sink.go	MySQL writers, conflict detection, active-active synchronization, and sink shutdown use the MySQL metrics package.
Remove legacy metric ownership pkg/metrics/sink.go, pkg/metrics/statistics.go	Removed MySQL-specific metric declarations, registrations, row-affected storage, recording methods, and cleanup logic.
Centralize encoder queue metrics pkg/sink/codec/encoder_group.go, pkg/sink/codec/metrics.go	A dedicated goroutine collects input and output queue gauges. Cleanup removes all labeled queue series.

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

Possibly related issues

• sink: make sink statistics consistent and flush-aware #5820 — Covers related MySQL affected-row metrics and statistics ownership changes.

Possibly related PRs

• pingcap/ticdc#5801 — Moves related statistics and metrics ownership into the MySQL sink package.

Suggested labels: lgtm, approved

Suggested reviewers: hongyunyan, wk989898

Poem

A rabbit counts each row with care,
MySQL metrics gather there.
Shared labels take a public name,
Queue gauges join the counting game.
Old counters clear at shutdown’s call.
Hop, hop—the metrics cover all.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The encoder-group metric collection and cleanup changes in pkg/sink/codec are unrelated to issue #5867.	Remove the unrelated pkg/sink/codec changes or link an issue that requires the encoder-group metric updates.
Docstring Coverage	⚠️ Warning	Docstring coverage is 43.75% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes satisfy issue #5867 by relocating MySQL metrics, moving affected-row recording to the writer, preserving Prometheus contracts, and managing series cleanup.
Title check	✅ Passed	The title clearly and concisely describes the main change: moving MySQL-only metrics into the MySQL sink package.
Description check	✅ Passed	The description follows the required template and explains the problem, implementation, tests, compatibility, documentation, and release note.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@pkg/sink/mysql/metrics_test.go`:
- Around line 49-50: Update the assertion after
DeleteDMLEventRowsAffectedMetrics(changefeedID) to expect a collected series
count of 1, reflecting that only the otherChangefeedID actual/insert series
remains.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: a41bec11-9da2-4f38-aa6e-1f5803cbd320

📥 Commits

Reviewing files that changed from the base of the PR and between af33cc1 and c9b87ad.

📒 Files selected for processing (19)

• downstreamadapter/sink/mysql/causality/conflict_detector.go
• downstreamadapter/sink/mysql/sink.go
• pkg/metrics/changefeed.go
• pkg/metrics/ddl.go
• pkg/metrics/dispatcher.go
• pkg/metrics/dynamic_stream.go
• pkg/metrics/init.go
• pkg/metrics/log_coordinator.go
• pkg/metrics/maintainer.go
• pkg/metrics/redo.go
• pkg/metrics/scheduler.go
• pkg/metrics/sink.go
• pkg/metrics/statistics.go
• pkg/sink/mysql/metrics.go
• pkg/sink/mysql/metrics_test.go
• pkg/sink/mysql/mysql_writer.go
• pkg/sink/mysql/mysql_writer_dml_exec.go
• pkg/sink/mysql/mysql_writer_for_active_active_sync_stats.go
• server/metrics.go

[3AceShowHand]

/test all

[3AceShowHand]

/test all

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hongyunyan, wk989898

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [hongyunyan,wk989898]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-08-04 06:57:44.286996265 +0000 UTC m=+2511250.323091321: ☑️ agreed by hongyunyan.
• 2026-08-04 07:34:17.481755608 +0000 UTC m=+2513443.517850664: ☑️ agreed by wk989898.

[ti-chi-bot]

@3AceShowHand: The following test 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-cdc-mysql-integration-light-next-gen-legacy-safepoint	9803a56	link	unknown	/test pull-cdc-mysql-integration-light-next-gen-legacy-safepoint

Full PR test history. Your PR dashboard.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.