distsql: avoid false positive error log about invalid cop task execution summaries length (#28188)

[ti-srebot]

cherry-pick #28188 to release-5.1
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/28263

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb.git pr/28263:release-5.1-e60f20b9f4ee

---

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary:
If TiDB is running query in MPP mode, there may be many error log about invalid cop task execution summaries length, it often makes user confused.

What is changed and how it works?

Proposal: xxx

What's Changed:

How it Works:

In fact, for streaming rpc to TiFlash(BatchCop and MPP), it is by design that only the last response will carry the execution summaries, so it is ok if some responses have no execution summaries, should not trigger an error log in this case.

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

Avoid false positive error log about `invalid cop task execution summaries length` when running MPP query.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• ichn-hu
• windtalker

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[ti-srebot]

/run-all-tests

[ti-srebot]

@windtalker you're already a collaborator in bot's repo.

[windtalker]

/merge

[ti-chi-bot]

@windtalker: /merge in this pull request requires 2 approval(s).

In response to this:

/merge

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[windtalker]

LGTM

[windtalker]

/merge

[ti-chi-bot]

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

Commit hash: 05788e6

[windtalker]

/run-mysql-test