ddl: limit the concurrent number of ingest jobs to 1 (#43210)

[ti-chi-bot]

This is an automated cherry-pick of #43210

What problem does this PR solve?

Issue Number: close #42903

Problem Summary:

What is changed and how it works?

• Add a unit test for pickBackfillType.
• Register the backend context immediately after checking the env is available.
• For some of the errors, we don't fall back to txn-merge mode anymore.
• Add a pre-check that if the disk available space is less than 10%, an error is reported.

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:

• Benjamin2037
• wjhuang2016

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[Benjamin2037]

LGTM

[tangenta]

/merge

[ti-chi-bot]

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

Commit hash: d020b28