[DNM] do delete range on each checkpoint update

[lidezhu]

What problem does this PR solve?

Issue Number: close #xxx

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Please refer to [Release Notes Language Style Guide](https://pingcap.github.io/tidb-dev-guide/contribute-to-tidb/release-notes-style-guide.html) to write a quality release note.

If you don't think this PR needs a release note then fill it with `None`.

[ti-chi-bot]

[FORMAT CHECKER NOTIFICATION]

Notice: To remove the do-not-merge/needs-linked-issue label, please provide the linked issue number on one line in the PR body, for example: Issue Number: close #123 or Issue Number: ref #456.

_{📖 For more info, you can check the "Contribute Code" section in the development guide.}

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign wlwilliamx for approval. For more information see the Code Review Process.
Please ensure that each of them provides their approval before proceeding.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[gemini-code-assist]

Summary of Changes

Hello @lidezhu, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refines the event store's checkpoint update process by removing a conditional check for adding garbage collection items. Previously, the system would only add a GC item if DML events occurred after the old checkpoint. The updated logic ensures that a garbage collection item is always registered when the dispatcher checkpoint is updated, simplifying the code and potentially enhancing the consistency of data cleanup operations.

Highlights

• Garbage Collection Logic Simplification: The conditional check that determined whether to add a garbage collection item based on the lastReceiveDMLTime has been removed from the UpdateDispatcherCheckpointTs function.
• Unconditional GC Item Addition: The addGCItem function is now called unconditionally every time the dispatcher checkpoint timestamp is updated, ensuring that garbage collection is always considered for the updated range.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request removes a buggy optimization that was intended to skip garbage collection tasks in the event store. The original logic incorrectly used lastReceiveDMLTime (a wall-clock time) to determine if there was data to GC, which is unreliable and could lead to GC being skipped when data should have been cleaned up. By removing this conditional block, a GC task is now always scheduled upon checkpoint updates, which is a safer and more correct approach, preventing potential storage bloat from un-collected data.

I am having trouble creating individual review comments. Click here to see my feedback.

logservice/eventstore/event_store.go (722-736)

This optimization logic is flawed. It compares lastReceiveDMLTime (a wall-clock time) with the physical time of oldCheckpointTs. This is unreliable due to potential clock drift between nodes and processing delays within the system.

A scenario where this fails:

1. A DML event with commit timestamp ts_commit is processed at wall-clock time T_process. lastReceiveDMLTime is updated to T_process.
2. The system goes idle, and no new DMLs are received.
3. UpdateDispatcherCheckpointTs is called later. The new oldCheckpointTs could correspond to a physical time greater than T_process.
4. The check lastReceiveDMLTime >= oldCheckpointPhysicalTime.UnixMilli() would then fail, and GC for a range that contains the DML event (with ts_commit) would be skipped incorrectly.

Removing this conditional and always scheduling a GC task is the correct and safer approach to prevent data from being missed by the garbage collector.