ddl: fix unexpected duplicate entry error when adding unique index

[tangenta]

What problem does this PR solve?

Issue Number: close #56161

Problem Summary: when merge-temp-index workers check duplicate index keys, they use BatchGet() to get index KV from the origin index and record them as a map. However, this map is not updated while handling temp index records, there may be a false-positive detection.

For example, we have {key_1 -> handle_1, key_2 -> handle_2}. If there is a temp index record like key_1 -> handle_3, then there is a duplicate key.

In this issue, we have two temp index records:

key_1 -> handle_1(deleted)
key_1 -> handle_2

The first record passes the check because a delete operation cannot cause a duplicate key. The second record fails the check because handle_2 != handle_1, even if handle_1 is deleted in the previous operation.

What changed and how does it work?

Maintain the map while handling, and remove the delete keys if necessary.

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

[tiprow]

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[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.

Project coverage is 57.0243%. Comparing base (c13eb90) to head (1f6bafb).
Report is 285 commits behind head on master.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #56162         +/-   ##
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- Coverage   72.9321%   57.0243%   -15.9079%     
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  Files          1611       1761        +150     
  Lines        447557     639313     +191756     
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+ Hits         326413     364564      +38151     
- Misses       101153     249795     +148642     
- Partials      19991      24954       +4963     

Flag	Coverage Δ
integration	40.3796% <64.7058%> (?)
unit	72.0600% <88.2352%> (+0.0491%)	⬆️

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Components	Coverage Δ
dumpling	52.9567% <ø> (ø)
parser	∅ <ø> (∅)
br	63.1196% <ø> (+17.2166%)	⬆️

[Benjamin2037]

LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-09-19 12:17:00.862277633 +0000 UTC m=+1136290.602701572: ☑️ agreed by wjhuang2016.
• 2024-09-20 07:42:11.183277862 +0000 UTC m=+1206200.923701801: ☑️ agreed by Benjamin2037.

[lance6716]

Suggested change

	// - if the handles matche, we can delete the index key.
	// - if the handle matches, we can delete the index key.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, lance6716, wjhuang2016

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #56264.

[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against pingcap/tidb#release-7.1 from head ti-chi-bot:cherry-pick-56162-to-release-7.1: the GitHub API request returns a 403 error: {"message":"You have exceeded a secondary rate limit and have been temporarily blocked from content creation. Please retry your request again later. If you reach out to GitHub Support for help, please include the request ID ACA6:3F108B:1B76053:33BE970:671F4644 and timestamp 2024-10-28 08:07:33 UTC.","documentation_url":"https://docs.github.com/rest/overview/rate-limits-for-the-rest-api#about-secondary-rate-limits","status":"403"}

[MimeLyc]

/cherry-pick release-7.1

[ti-chi-bot]

@MimeLyc: new pull request created to branch release-7.1: #57225.

In response to this:

/cherry-pick release-7.1

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