0429 maintainer skip syncpoint

[asddongmen]

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[gemini-code-assist]

Code Review

This pull request introduces a mechanism to control Sync Point events in TiCDC, primarily to mitigate performance overhead during periods of high replication lag. It adds SyncPointControl and SyncPointControlMessage to the heartbeat protocol, enabling the maintainer to broadcast skip windows to dispatchers. Corresponding logic is implemented in the DispatcherManager and BasicDispatcher to skip events within these windows, and the maintainer's Barrier is updated to support direct passing of Sync Points when lag exceeds defined thresholds. Feedback on the implementation highlighted a critical safety issue in the SyncPointControlMessageHandler, where the code would panic if multiple messages were batched by the dynstream framework; a suggestion was provided to process the most recent message instead.

[gemini-code-assist]

The Handle method for SyncPointControlMessageHandler should not panic if the number of messages is not exactly one. The dynstream framework can batch multiple events for the same path into a single Handle call if they are queued. Panicking in production code due to unexpected batching is dangerous. Instead, you should process all messages in the batch or at least the most recent one (the last one in the slice) to ensure the dispatcher manager stays in sync with the maintainer's desired state.

func (h *SyncPointControlMessageHandler) Handle(dispatcherManager *DispatcherManager, messages ...SyncPointControlMessage) bool {
	if len(messages) > 0 {
		dispatcherManager.SetSyncPointControl(messages[len(messages)-1].Control)
	}
	return false
}