Fix ddl barrier backlog

[haiboumich]

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Issue Number: close #xxx

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[gemini-code-assist]

Code Review

This pull request improves the handling of handshake events to unblock idle tables and optimizes barrier tracking in the maintainer to prevent memory growth during DDL-heavy workloads by waiting for the DDL dispatcher's report. The feedback identifies an issue where the deferredStatus flag is incorrectly placed, potentially leading to spurious warning logs. Additionally, it is suggested to expand the barrier deferral logic to include InfluenceType_All (syncpoints) to further mitigate memory growth issues and to update log messages accordingly.

[gemini-code-assist]

The deferredStatus flag is currently only set when event == nil. However, handleOneStatus can return a non-nil event with needACK == false (for example, in handleBlockState at lines 432 and 466 when an event is deferred due to pending schedule events or scheduling not being ready). In these cases, deferredStatus remains false, which will trigger a spurious "no dispatcher status to send" warning log at line 156 if no other statuses are processed in the request.

Consider setting deferredStatus = true and continuing the loop whenever needACK is false to correctly handle all deferred status paths.

Suggested change

	if event == nil {
	if !needACK {
	deferredStatus = true
	continue
	}
	if !needACK {
	deferredStatus = true
	continue
	}
	if event == nil {

[gemini-code-assist]

If the helper function is updated to include InfluenceType_All (syncpoints), the log message and function call should be updated to reflect that it now covers more than just 'normal' block events.

Suggested change

	normalBlockEventIncludesDDLSpan(blockState.BlockTables) {
	log.Debug("wait ddl dispatcher report before tracking normal block event",
	blockEventIncludesDDLSpan(blockState.BlockTables) {
	log.Debug("wait ddl dispatcher report before tracking block event",

[gemini-code-assist]

The current implementation only defers InfluenceType_Normal events that include the DDL span. However, InfluenceType_All events (such as syncpoints) also conceptually include the DDL span and are coordinated by the DDL dispatcher. If there is a large backlog of syncpoints, table dispatchers reporting them before the DDL dispatcher will still create BarrierEvent objects, which could lead to the memory growth issue this PR aims to address.

Consider renaming this function to blockEventIncludesDDLSpan and including InfluenceType_All in the check.

func blockEventIncludesDDLSpan(blockedTables *heartbeatpb.InfluencedTables) bool {
	if blockedTables == nil {
		return false
	}
	if blockedTables.InfluenceType == heartbeatpb.InfluenceType_All {
		return true
	}
	if blockedTables.InfluenceType != heartbeatpb.InfluenceType_Normal {
		return false
	}
	for _, tableID := range blockedTables.TableIDs {
		if tableID == common.DDLSpanTableID {
			return true
		}
	}
	return false
}

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