ddl: refactor schema builder

[xhebox]

What problem does this PR solve?

Issue Number: ref #30272

Problem Summary: Sub task from #28763. The big function ApplyDiff is separated into two parts: the outer one serve as the first dispatching layer, which will handle some loosely-related actions; all other actions falls into default, which either requires applyUpdateTable(the original main logic of ApplyDiff) to update the infoschema, or process AffectedOpts.

It is made very clear and verbose about how the actions are handled. The redundant code is intended to make it clear.

Also one memory optimization is applied, dbInfo won't be copied every time in applyUpdateTable.

copySchemaTables is renamed to getSchemaAndCopyIfNecessary.

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

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• AilinKid
• wjhuang2016

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[AilinKid]

LGTM, pls add tests for it either in this one or next pull request

[xhebox]

LGTM, pls add tests for it either in this one or next pull request

Thx, I don't think new tests are needed. It is same as before anyway. But I think some failed tests may be related, I'll take a deeper look...

[wjhuang2016]

/merge

[xhebox]

/merge cancel

[xhebox]

Seems stable, I am looking at it.

[xhebox]

Since my fix for rename tables, auto id allocated are not as expected as in the tests. It should not be "1,2,3" but "1,5001", which is the result reusing allocators.3

[xhebox]

/merge

[ti-chi-bot]

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

Commit hash: 7f4d41e

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/6f42e215fe76c63fb7cbd8d38a62baff87b488d3

[ti-chi-bot]

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[xhebox]

/merge