ddl: skip deleting the unmatched index key on merge (#40465)

[ti-chi-bot]

This is an automated cherry-pick of #40465

What problem does this PR solve?

Issue Number: close #40464

Problem Summary:

create table t (a int, b int);
alter table t add unique index idx(a);

-- delete only:
insert into t values (5, 5);

-- write only:
insert into t values (5, 7);
delete from t where b = 7;

In write-only state, the first insert statement wrote a kv {5->r_6} and updates it to {5->deleted} immediately. This operation is incorrectly applied during the merge of temp index. As a result, the index to (5, 5) is missing.

What is changed and how it works?

When TiDB merges the temp indexes, it should check whether the index to be deleted matches against the handle in the deletion marker kv. If they don't match, TiDB can skip it directly.

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

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

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• wjhuang2016
• zimulala

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[tangenta]

/merge

[ti-chi-bot]

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

Commit hash: 73e469f

[ti-chi-bot]

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[tangenta]

/retest