execution: fix the incorrect use of cached plan for point get (#24749)

[ti-srebot]

cherry-pick #24749 to release-4.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/24764

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git push [email protected]:ti-srebot/tidb.git pr/24764:release-4.0-f71fbdb179f6

---

Signed-off-by: cfzjywxk [email protected]

What problem does this PR solve?

Issue Number: close #24741

Problem Summary:
The point get cached plan is used incorrectly for the in transaction prepare execution statement, which may change the transaction to invalid status unexpectedly and lead to panic or incorrect read.

What is changed and how it works?

What's Changed:
Use the autocommitTxn judge logic instead of autocommit.

How it Works:
The autocommit mode flag and the in txn flag are different. In the IsCachedExecOk logic, only autocommit primary key point get read could use the cached plan.

Related changes

Check List

Tests

• Unit test

Side effects

Release note

• Fix the issue point get cached plan of prepared statement is incorrectly used by in transaction point get statement.

[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-srebot]

/run-all-tests

[jackysp]

lgtm

[lysu]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• jackysp
• lysu

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[cfzjywxk]

/merge

[ti-chi-bot]

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

Commit hash: 2161992

[ti-chi-bot]

@ti-srebot: Your PR was out of date, I have automatically updated it for you.

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