sessionctx,executor: introduce @@tidb_active_active_sync_stats variable for TiCDC | tidb-test=feature/active-active tikv=feature/active-active

[tiancaiamao]

…le for TiCDC

What problem does this PR solve?

Issue Number: ref #65269

Problem Summary:

What changed and how does it work?

Provide a new system variable to read it.

SELECT @@tidb_active_active_sync_stats;
+---------------------------------+
| @@tidb_active_active_sync_stats |
+---------------------------------+
| {"conflict_skip_rows": 123 }    |
+---------------------------------+

The CDC can query this variable periodically (.i.e, 5 minutes) to update the metrics. Because one TiDB connection only serves one changefeed, we only need to record a single count per connection.

Check List

Tests

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

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

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Codecov Report

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[lcwangchao]

Rest LGTM

[tiancaiamao]

/retest

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[time-and-fate]

So we don't need to clear or reset this count?

[tiancaiamao]

Yes, no reset.
Each session has a session variable tidb_cdc_active_active_sync_stats, ticdc can check it and compare the value with previous value to know the metrics in a period.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: lcwangchao, time-and-fate
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Details

Needs approval from an approver in each of these files:

• OWNERS [lcwangchao,time-and-fate]
• pkg/sessionctx/vardef/OWNERS
• pkg/sessionctx/variable/OWNERS

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-12-29 09:51:55.438122318 +0000 UTC m=+4671.256430740: ☑️ agreed by lcwangchao.
• 2025-12-30 03:34:46.03579577 +0000 UTC m=+68441.854104202: ☑️ agreed by time-and-fate.

[tiancaiamao]

/retest

[tiprow]

@tiancaiamao: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

Details

In response to this:

/retest

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