[FLINK-7245] Enhance the operators to support holding back watermarks

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Implemented
• Fix Version/s: 1.4.0
• Component/s: API / DataStream
• Assignee: Xingcan Cui
• Reporter: Xingcan Cui
• Created: 23/Jul/17 12:41
• Updated: 29/Aug/17 20:16
• Resolved: 29/Aug/17 20:16

Description

Currently the watermarks are applied and emitted by the AbstractStreamOperator instantly.

public void processWatermark(Watermark mark) throws Exception {
	if (timeServiceManager != null) {
		timeServiceManager.advanceWatermark(mark);
	}
	output.emitWatermark(mark);
}

Some calculation results (with timestamp fields) triggered by these watermarks (e.g., join or aggregate results) may be regarded as delayed by the downstream operators since their timestamps must be less than or equal to the corresponding triggers.

This issue aims to add another "working mode", which supports holding back watermarks, to current operators. These watermarks should be blocked and stored by the operators until all the corresponding new generated results are emitted.

Issue Links

• links to: GitHub Pull Request #4530