log-backup: fix early return

[YuJuncen]

What is changed and how it works?

Issue Number: Close #13281

What's Changed:
This PR fixed a bug that may cause data loss with the satisfaction of these conditions:

• In the initial scanning stage, if...
  • There are more than 1,024 adjacent keys are prewritten but not committed.
  • The values of these keys are all short enough to be inlined in the write CF.
    ("adjacent" means, the initial scanning cannot get any commit entries interleaving them, the DeltaScanner emits a batch with 1,024 Prewrites).
• If there are some keys committed BEFORE the initial scanning but NOT YET have been observed, those key would be lost. (For a detailed case, check the integration test split_txn).

Fixed a bug that may cause data loss in log backup.

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Integration test
• Manual test (add detailed scripts or steps below)
  We have tested this with 1,000 tables in sysbench oltp_write_only prepare phase.
  • with this PR, no data loss observed.
  • without this PR, there would always be data loss for some tables.

Release note

Fixed a bug that may cause PiTR losing some data when there are too many adjacent short row putting.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• 3pointer
• overvenus

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[YuJuncen]

/cc @hicqu @overvenus @3pointer

[overvenus]

How the "weird transactions" looks like? Could you add some comments?

[3pointer]

LGTM

[overvenus]

/merge

[ti-chi-bot]

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[ti-chi-bot]

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

Commit hash: 6b5a8c3

[ti-srebot]

cherry pick to release-6.2 in PR #13291