[GitHub] [spark] viirya commented on a change in pull request #35362: [SPARK-38069][SQL][SS] Improve the calculation of time window

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viirya commented on a change in pull request #35362:
URL: https://github.com/apache/spark/pull/35362#discussion_r801353720



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
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@@ -3843,8 +3843,8 @@ object TimeWindowing extends Rule[LogicalPlan] {
    * The windows are calculated as below:
    * maxNumOverlapping <- ceil(windowDuration / slideDuration)
    * for (i <- 0 until maxNumOverlapping)
-   *   windowId <- ceil((timestamp - startTime) / slideDuration)
-   *   windowStart <- windowId * slideDuration + (i - maxNumOverlapping) * slideDuration + startTime
+   *   lastStart <- timestamp - (timestamp - startTime + windowDuration) % windowDuration

Review comment:
       Hmm, I suppose this is the window start time of last window. Don't we need to consider slide duration when calculating last start? I think this is only correct if the slide duration equals to window duration. 




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