PiTR: support empty schema in PiTR.

[joccau]

Signed-off-by: joccau zak.zhao@pingcap.com

What problem does this PR solve?

Issue Number: ref #33866

Problem Summary:

What is changed and how it works?

Support empty schema in PiTR.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

test

• backup steps

  • create empty schema emptydb
  • br backup full in up-stream
  • br log start in up-stream
  • create table emptydb.t and insert 1000 record.

• restore steps 1

• br restore point --full-backup-storage --s in down-stream. emptydb.t and records has been recovered.

• restore steps 2

• br restore full in down-stream

• br restore point --start-ts --restore-ts in down-stream. emptydb.t and records has been recovered.

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]

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• 3pointer

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[joccau]

/cc @3pointer @YuJuncen PTAL

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/cc @3pointer @YuJuncen PTAL

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[joccau]

/run-unit-test

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/4de3284040e7733ed0040866a5f67eadcb9d9042