txn: fix the panic when memdb grows beyond quota

[ekexium]

Signed-off-by: ekexium eke@fastmail.com

What problem does this PR solve?

Issue Number: close #39611

Problem Summary:
The sequence of events that leads to the panic is:
membuffer.set -> enlarge -> onMemChange -> memory tracker decides to panic -> deferred releasing current staging buffer in AddRecord -> revert to last checkpoint

When reverting to last checkpoint, memdb iterates over the nodes backwards, here is why it panics:
The latest block of the arena is in an intermediate state: it is just allocated but no data has been written yet. So its length is 0. While during the iteration we assume the length cannot be 0.

What is changed and how it works?

Don't let memdb call the callback when the block is in intermediate state. Instead call it after any content is inserted after a new block is allocated.

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

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• sticnarf
• you06

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[gengliqi]

/build

[sticnarf]

LGTM.
@gengliqi Please help confirm whether the issue is fixed. Thanks.

[gengliqi]

My test result shows this PR has fixed #39611

[ti-chi-bot]

@gengliqi: Thanks for your review. The bot only counts approvals from reviewers and higher roles in list, but you're still welcome to leave your comments.

In response to this:

My test result shows this PR has fixed #39611

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[ekexium]

/merge

[ti-chi-bot]

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

Commit hash: 446b779

[ekexium]

/run-unit-test

[ekexium]

/run-unit-test

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #39640.

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! New failing [2] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/common-test	🟥 failed 1, success 10, total 11	10 min	New failing
idc-jenkins-ci-tidb/sqllogic-test-1	🟥 failed 1, success 25, total 26	3 min 51 sec	New failing
idc-jenkins-ci/integration-cdc-test	🔴 failed 1, success 39, total 40	19 min	Existing failure
idc-jenkins-ci-tidb/integration-common-test	🟢 all 17 tests passed	15 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	5 min 46 sec	Existing passed
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	4 min 47 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	4 min 32 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	3 min 55 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 0 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed