executor: fix correctness of hash join v2 when there are multiple var-length keys

[windtalker]

What problem does this PR solve?

Issue Number: close #55016

Problem Summary:

HashJoinV2, it will first pack all the join keys into a byte array named serializedKey, and during the probe stage, it will compare serializedKey directly, if the serializedKey matches, the join think its original key matches. codec.SerializeKeys is used to generate serializedKey, for var-length column, if SerializeMode is not keepStringLength, it will not record string length in serializedKey.
Currently, only a string key is inlined, it need to record string length.
The problem is if the join key is 2 strings like a = a and b = b, if string length is not kept in serializedKey, then the following two pair of keys will generate same serializedKey
{a: aa, b: a}
{a: a, b: aa}
which is not expected.
In this pr, it always record var-column length into serialized key except all the following condition is true

• the join key only contains 1 var length column
• the join key is not inlined

In the above case, since there is only 1 var length column, it is ok to discard the var-column length in serializedKey because we will record the total length of serializedKey.

What changed and how does it work?

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 63.46154% with 19 lines in your changes missing coverage. Please review.

Project coverage is 73.8921%. Comparing base (0ad2ca6) to head (220a896).
Report is 25 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #55080        +/-   ##
================================================
+ Coverage   72.8125%   73.8921%   +1.0795%     
================================================
  Files          1561       1568         +7     
  Lines        438809     447834      +9025     
================================================
+ Hits         319508     330914     +11406     
+ Misses        99605      96605      -3000     
- Partials      19696      20315       +619     

Flag	Coverage Δ
integration	70.7090% <63.4615%> (?)
unit	71.6845% <63.4615%> (-0.1270%)	⬇️

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Components	Coverage Δ
dumpling	52.9567% <ø> (ø)
parser	∅ <ø> (∅)
br	52.5488% <ø> (+6.6521%)	⬆️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: wshwsh12, XuHuaiyu

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-07-31 05:01:04.906815747 +0000 UTC m=+331981.186863818: ☑️ agreed by wshwsh12.
• 2024-08-02 03:37:32.69615505 +0000 UTC m=+60649.914916658: ☑️ agreed by XuHuaiyu.