ddl: fix ALTER TABLE NOCACHE not removing record from mysql.table_cache_meta

[expxiaoli]

What problem does this PR solve?

Issue Number: close #66042

Problem Summary:

When executing ALTER TABLE t NOCACHE, TiDB correctly updates the table's TableCacheStatusType to Disable, but does not delete the corresponding row from mysql.table_cache_meta. As a result, after ALTER TABLE NOCACHE, the stale record remains in mysql.table_cache_meta (with lock_type = READ if a SELECT was issued while the table was cached), violating the expected invariant that cached-table metadata only exists for tables currently in cache mode.

What changed and how does it work?

In finishDDLJob (pkg/ddl/job_worker.go), added a new case for ActionAlterNoCacheTable: when the job completes successfully, delete the row for the table from mysql.table_cache_meta. This mirrors the insert done during ALTER TABLE CACHE (in executor.go) and ensures the two operations stay symmetric.

Check List

Tests

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

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

Fix `ALTER TABLE NOCACHE` not removing the stale record from `mysql.table_cache_meta`.

Summary by CodeRabbit

• Bug Fixes
  • Fixed improper removal of table cache metadata when executing ALTER TABLE NOCACHE, ensuring cache entries are properly cleaned up and no orphaned metadata remains.

[pantheon-ai]

Review Complete

Findings: 0 issues
Posted: 0
Duplicates/Skipped: 0

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 8184cf3a-93c4-4e57-a656-d31cc9c63f31

📥 Commits

Reviewing files that changed from the base of the PR and between 0f00d92 and c412273.

📒 Files selected for processing (2)

• pkg/ddl/db_cache_test.go
• pkg/ddl/job_worker.go

---

📝 Walkthrough

Walkthrough

The changes implement a fix for ALTER TABLE NOCACHE to properly remove the corresponding entry from the mysql.table_cache_meta table. A new DDL job handler branch executes cleanup SQL to delete the cache metadata record, accompanied by a test verifying the removal behavior.

Changes

Cohort / File(s)	Summary
ALTER TABLE NOCACHE cache cleanup pkg/ddl/job_worker.go, pkg/ddl/db_cache_test.go	Added DDL job handler for ActionAlterNoCacheTable that executes cleanup SQL to remove the table entry from mysql.table_cache_meta, with a corresponding test validating the metadata record is properly deleted after ALTER TABLE NOCACHE.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 A cache that fades without a trace,
No orphaned rows cluttering the space,
When NOCACHE is set with gentle might,
Metadata vanishes—squeaky clean and right! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: fixing ALTER TABLE NOCACHE not removing records from mysql.table_cache_meta, which is the primary objective of the PR.
Description check	✅ Passed	The description follows the template with clear problem statement, solution explanation, and appropriate checkboxes marked; includes issue reference #66042 and a release note.
Linked Issues check	✅ Passed	The code changes fully address issue #66042 by adding a delete operation in finishDDLJob for ActionAlterNoCacheTable and including a unit test to verify the mysql.table_cache_meta row is deleted.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the ALTER TABLE NOCACHE bug: one file adds a unit test and another adds the cleanup logic in DDL job handling.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

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📝 Coding Plan

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[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.5145%. Comparing base (102f7af) to head (c412273).
⚠️ Report is 41 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #67109        +/-   ##
================================================
+ Coverage   77.7098%   80.5145%   +2.8047%     
================================================
  Files          2016       1968        -48     
  Lines        552001     555589      +3588     
================================================
+ Hits         428959     447330     +18371     
+ Misses       121300     106794     -14506     
+ Partials       1742       1465       -277     

Flag	Coverage Δ
integration	48.6292% <57.1428%> (+0.5024%)	⬆️
unit	77.6974% <71.4285%> (+1.4460%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	63.6984% <ø> (+6.6885%)	⬆️
parser	∅ <ø> (∅)
br	68.5750% <ø> (+7.7605%)	⬆️

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[expxiaoli]

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[expxiaoli]

/retest-required

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[pantheon-ai]

✅ Code looks good. No issues found.

[expxiaoli]

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: tiancaiamao, wjhuang2016

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-03-23 06:11:32.977088932 +0000 UTC m=+162289.013159192: ☑️ agreed by wjhuang2016.
• 2026-03-23 09:28:19.878642652 +0000 UTC m=+174095.914712922: ☑️ agreed by tiancaiamao.

[expxiaoli]

/retest-required

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[expxiaoli]

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