[WIP] optimize memory control

[lidezhu]

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Issue Number: close #xxx

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[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 introduces an adaptive mechanism to optimize memory control within the EventCollector by dynamically adjusting the data scanning interval for changefeeds. This system monitors memory usage and, in response to high memory pressure, can reduce the scanMaxTs to limit the amount of data being processed. Conversely, it can increase the scan interval when memory is abundant. The changes involve new components for adaptive window logic, updates to the congestion control messaging to include the scanMaxTs, and modifications to the event broker to enforce these dynamic scan limits, ultimately aiming to prevent out-of-memory issues and improve system stability under varying loads.

Highlights

• Adaptive Scan Window: Introduced a new adaptiveScanWindow mechanism to dynamically adjust the data scanning interval for changefeeds based on their memory usage ratio. This window can grow, shrink, or reset based on predefined thresholds and observation periods.
• Memory Control Integration: Integrated the adaptive scan window into the EventCollector to calculate and propagate a scanMaxTs for each changefeed. This scanMaxTs acts as an upper bound for data scanning, effectively slowing down data ingestion when memory pressure is high.
• Congestion Control Protocol Update: Updated the CongestionControl message protocol to version 2, adding a ScanMaxTs field to the AvailableMemory message. This allows the EventCollector to communicate the dynamically calculated scan limit to the EventBroker.
• Event Broker Enforcement: The EventBroker now receives and respects the scanMaxTs from the EventCollector. When determining the data range for a scan task, it will adjust the CommitTsEnd to scanMaxTs if a limit is active, or even skip scanning entirely if the scan window is fully consumed.

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[gemini-code-assist]

Code Review

This pull request introduces an adaptive scan window mechanism to optimize memory control, which is a great initiative. The core logic in adaptive_scan_window.go dynamically adjusts the scan interval based on memory usage, with thresholds for growing, shrinking, and resetting the window. This is then integrated into the event collector to control the scanMaxTs sent via congestion control messages. The changes to the congestion control protocol to support scanMaxTs are well-implemented with versioning for backward compatibility.

My review focuses on simplifying some of the new logic for better maintainability. I've left a couple of suggestions in adaptive_scan_window.go to make the clamping logic more concise and to remove a redundant code block.

The tests for the new adaptive window logic and the updated congestion control protocol are thorough and cover the main scenarios. Overall, this is a solid implementation of the memory optimization strategy.

[gemini-code-assist]

This block for clamping maxInterval can be simplified. The check for maxInterval <= 0 is covered by maxInterval < adaptiveScanWindowMin since adaptiveScanWindowMin is a positive duration (1s). You can make this more concise.

Suggested change

	if maxInterval <= 0 {
	maxInterval = adaptiveScanWindowMin
	}
	if maxInterval > adaptiveScanWindowMax {
	maxInterval = adaptiveScanWindowMax
	}
	if maxInterval < adaptiveScanWindowMin {
	maxInterval = adaptiveScanWindowMin
	}
	if maxInterval > adaptiveScanWindowMax {
	maxInterval = adaptiveScanWindowMax
	}
	if maxInterval < adaptiveScanWindowMin {
	maxInterval = adaptiveScanWindowMin
	}

[gemini-code-assist]

This final clamping of w.interval appears to be redundant. The logic for shrinking (line 93) and growing (line 99) the interval already ensures that w.interval remains within the [adaptiveScanWindowMin, maxInterval] bounds by using max() and min(). You can safely remove this block to simplify the code.

[ti-chi-bot]

@lidezhu: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-check	492f361	link	true	/test pull-check

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