executor: Fix a panic when using on duplicate update (#31287)

[ti-srebot]

cherry-pick #31287 to release-5.1
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/31342

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git push git@github.com:ti-srebot/tidb.git pr/31342:release-5.1-42e009a53873

---

What problem does this PR solve?

Issue Number: close #28078

Problem Summary: When using statements like insert into a select ... from b on duplicate key update a.y = b.y, where b.y is not selected in select ... from b part, sometimes it may panic and reports "slice bounds out of range".

initEvalBuffer4Dup constructs a list of column types (the evalBufferTypes variable), which is expected to match the Schema4OnDuplicate built in function Schema4OnDuplicate. It contains several parts sequentially:

• columns of already-existed rows
• extra columns to select (the implicitly required columns in the on duplicate key update clause)
• columns of new rows to insert

The problem is:

1. When constructing evalBufferTypes, wrong index is used to find the second part (extra columns to select) . The inner select plan contains both explicitly written columns in select clause (which are columns [:actualColLen]), and the implicitly required columns in the on duplicate key update clause (which are columns [actualColLen:]). In function initEvalBuffer4Dup, the actualColLen is exactly e.rowLen.
2. Then it creates a buffer for storing values to be inserted. It's expected to match the third part of evalBufferTypes mentioned above. However wrong index is used again and it didn't count the number of extra columns to the offset.

What is changed and how it works?

Fixed the above two mistakes.

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 a panic that may happen when using `on duplicate key update`.

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• cfzjywxk
• winoros

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[ti-srebot]

/run-all-tests

[ti-srebot]

@MyonKeminta you're already a collaborator in bot's repo.

[bb7133]

/merge

[ti-chi-bot]

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

Commit hash: 119cb4d