logpuller: add region task priority queue for subscription client

[asddongmen]

What problem does this PR solve?

Issue Number: close #1942

What is changed and how it works?

This pull request introduces a priority queue mechanism within the logpuller's subscriptionClient to manage region-related tasks. This enhancement allows the system to prioritize critical tasks, such as handling region errors or changes, over less urgent tasks like new region subscriptions, ensuring more efficient and responsive processing of events from TiKV.

Highlights

Prioritized Region Task Management: Implemented a new thread-safe PriorityQueue to manage region tasks, replacing the previous channel-based approach. This queue prioritizes tasks based on their type (e.g., high priority for region errors, low priority for new subscriptions) and the time they have spent waiting.
Dynamic Task Prioritization: Introduced PriorityTask and regionPriorityTask to define different task types and calculate their priority. Tasks gain higher priority (lower value) as they wait longer in the queue, preventing starvation of lower-priority tasks.

Enhanced subscriptionClient Logic: The subscriptionClient now utilizes this priority queue for scheduling region requests. Error handling paths (e.g., NotLeader, EpochNotMatch, RegionNotFound) now assign TaskErrorPrior to ensure immediate re-scheduling, while new subscriptions are assigned TaskLowPrior.

Comprehensive Unit Testing: New unit tests have been added for both the PriorityQueue and PriorityTask implementations, covering various scenarios including priority ordering, time-based prioritization, blocking/non-blocking operations, and concurrent access.

Codebase Refinement: Cleaned up unused metrics and struct fields within subscription_client.go to improve code clarity and maintainability.

Test Result

Before this PR, creating a changefeed (CF) that generates a large volume of incremental scan tasks would severely impact the resolvedTs lag of other changefeeds. Until the new CF completed incremental scans for all its associated regions, the lag of other CFs would keep rising—even leading to lags of several hours in severe cases.

This PR has greatly mitigated this issue: now, when a new changefeed with a large number of incremental scan tasks is created, it only causes a lag impact of several seconds to a few minutes on other changefeeds. The exact duration of the impact depends on the number of TiKV nodes and regions, as these factors determine how long it takes to complete the incremental scan task for a single region.

After:

Before:

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)

Questions

Will it cause performance regression or break compatibility?

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

Release note

None

[ti-chi-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[gemini-code-assist]

Summary of Changes

Hello @asddongmen, 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 introduces a priority queue mechanism within the logpuller's subscriptionClient to manage region-related tasks. This enhancement allows the system to prioritize critical tasks, such as handling region errors or changes, over less urgent tasks like new region subscriptions, ensuring more efficient and responsive processing of events from TiKV.

Highlights

• Prioritized Region Task Management: Implemented a new thread-safe PriorityQueue to manage region tasks, replacing the previous channel-based approach. This queue prioritizes tasks based on their type (e.g., high priority for region errors, low priority for new subscriptions) and the time they have spent waiting.
• Dynamic Task Prioritization: Introduced PriorityTask and regionPriorityTask to define different task types and calculate their priority. Tasks gain higher priority (lower value) as they wait longer in the queue, preventing starvation of lower-priority tasks.
• Enhanced subscriptionClient Logic: The subscriptionClient now utilizes this priority queue for scheduling region requests. Error handling paths (e.g., NotLeader, EpochNotMatch, RegionNotFound) now assign TaskHighPrior to ensure immediate re-scheduling, while new subscriptions are assigned TaskLowPrior.
• Comprehensive Unit Testing: New unit tests have been added for both the PriorityQueue and PriorityTask implementations, covering various scenarios including priority ordering, time-based prioritization, blocking/non-blocking operations, and concurrent access.
• Codebase Refinement: Cleaned up unused metrics and struct fields within subscription_client.go to improve code clarity and maintainability.

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[gemini-code-assist]

Code Review

This pull request introduces a priority queue for region tasks in the logpuller to better handle tasks like region errors and new subscriptions. The implementation of the priority queue, task prioritization, and its integration into the subscription client are well-structured. I've identified a high-severity bug in the PriorityQueue's Pop method that could lead to a busy-loop, along with a few medium-severity suggestions for improving code clarity, efficiency, and test robustness. Overall, this is a good addition that improves task handling logic.

[asddongmen]

/test all

[asddongmen]

/test all

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: 3AceShowHand
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-09-05 10:45:28.430117202 +0000 UTC m=+12594.989998719: ☑️ agreed by 3AceShowHand.