ddl: move backend register from backfillDistExecutor to its StepExecutor

[lance6716]

What problem does this PR solve?

Issue Number: ref #50752

Problem Summary:

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

  pass existing tests

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]

Hi @lance6716. Thanks for your PR.

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[ywqzzy]

#50744

[codecov]

Codecov Report

Merging #51247 (6a65c54) into master (9ee46d4) will decrease coverage by 15.9315%.
Report is 3 commits behind head on master.
The diff coverage is 72.6315%.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #51247         +/-   ##
=================================================
- Coverage   70.5917%   54.6602%   -15.9315%     
=================================================
  Files          1467       1577        +110     
  Lines        435011     602505     +167494     
=================================================
+ Hits         307082     329331      +22249     
- Misses       108658     250247     +141589     
- Partials      19271      22927       +3656     

Flag	Coverage Δ
integration	36.8117% <71.5789%> (?)
unit	70.3261% <2.1052%> (-0.0646%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9957% <ø> (ø)
parser	∅ <ø> (∅)
br	51.3833% <ø> (+5.4953%)	⬆️

[lance6716]

ping @ywqzzy

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: tangenta, ywqzzy

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• pkg/ddl/OWNERS [tangenta,ywqzzy]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-02-22 09:55:19.965797802 +0000 UTC m=+523808.713420913: ☑️ agreed by tangenta.
• 2024-02-22 10:32:31.063970456 +0000 UTC m=+526039.811593567: ☑️ agreed by ywqzzy.