ddl: fix concurrent column type changes(with changing data) that cause schema and data inconsistencies (#31051)

[ti-srebot]

cherry-pick #31051 to release-5.1
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/31069

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git push [email protected]:ti-srebot/tidb.git pr/31069:release-5.1-4ca3b02c90b7

---

What problem does this PR solve?

Issue Number: close #31048

Problem Summary:

For column type changes, the column ID is changed if it is lossy.

If both sessions perform lossy column type changes((like modify column c int -> char)) simultaneously

1. Connection1: execute DDL1, it will change column ID (ID :1-> ID :2)

2. Connection2: execute DDL2. After DDL1 enters the DDL job queue and is not executed, then DDL2 enters the job queue.

3. After DDL1 is executed successfully, DDL2 considers that the column is not lossy(char -> char), so it does not change the column ID, which is the old id:1. So id:1 overwrites id:2.

After DDL2 is completed, the column ID is still the original id:1 instead of the correct id:2.

Because the column ID was changed incorrectly, the schema could not match the data, resulting in decode failure when reading data.

What is changed and how it works?

In step 3, we check that the ID of the modified column is the same as the ID of the original column.

Check List

Tests

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

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 concurrent column type changes(with changing data) that cause schema and data inconsistencies.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• AilinKid
• tangenta

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[ti-srebot]

/run-all-tests

[ti-srebot]

@zimulala please accept the invitation then you can push to the cherry-pick pull requests. Comment with /cherry-pick-invite if the invitation is expired.
https://github.com/ti-srebot/tidb/invitations

[zimulala]

/run-mysql-test

[zimulala]

/run-mysql-test

[zimulala]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: e2666b3