[BEAM-3360] [SQL] Do not assign triggers for HOP/TUMBLE

• Type: Task
• Status: Resolved
• Priority: P2
• Resolution: Fixed
• Fix Version/s: 2.4.0
• Component/s: dsl-sql
• Assignee: Anton Kedin
• Reporter: Anton Kedin
• Created: 15/Dec/17 18:00
• Updated: 24/Jul/20 20:14
• Resolved: 13/Apr/18 16:41

Description

Currently when parsing HOP/TUMBLE/SESSION expressions we create a repeating trigger for the defined windows, see:

BeamAggregationRule.java

  private Trigger createTriggerWithDelay(GregorianCalendar delayTime) {
    return Repeatedly.forever(AfterWatermark.pastEndOfWindow().withLateFirings(AfterProcessingTime
        .pastFirstElementInPane().plusDelayOf(Duration.millis(delayTime.getTimeInMillis()))));
  }

This will not work correctly with joins, as joins with multiple trigger firings are currently broken: https://issues.apache.org/jira/browse/BEAM-3190 .

Even if joins with multiple firings worked correctly, SQL parsing stage is still probably an incorrect place to infer them.

Better alternatives:

• inherit the user-defined triggers for the input pcollection without modification;
• triggering at sinks ( https://s.apache.org/beam-sink-triggers ) might define a way to backpropagate triggers with correct semantics;

Issue Links

• blocks: BEAM-3345 [SQL] Reject Unsupported Joins
• relates to: BEAM-3190 [SQL] Join Windowing Semantics