shardddl/optimistic: use init-schema for table without info when recover lock (#1551)

[ti-srebot]

cherry-pick #1551 to release-2.0
You can switch your code base to this Pull Request by using git-extras:

# In dm repo:
git pr https://github.com/pingcap/dm/pull/1553

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git push [email protected]:ti-srebot/dm.git pr/1553:release-2.0-b6346dc1674c

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What problem does this PR solve?

In #1518, we always use table-info-before to rebuild locks, but ignore the upstream table who has no optimism.Info. In such a case, we may build an incorrect joined table.

Suppose there are two upstream tables tb1(a int, b int, c int) and tb2(a int, b int, c int). A possible time series is:

t1: tb1 and tb2 are identical.
t2: tb1 drop column b, c.
t3: restart.
t4: joined becomes tb1's table-info-before, which is tb(a int). // The correct joined should be tb(a int, b int, c int).

What is changed and how it works?

Use init-schema for table without info when recover lock. If there is no optimism.Info for a upstream table, it indicates the table structure hasn't been changed since last removeLock. So the init schema should be its table info.

Check List

Tests

• Unit test
• Integration test

[lance6716]

/lgtm

[ti-chi-bot]

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