[GitHub] [spark] xuanyuanking commented on a change in pull request #30427: [SPARK-33224][SS] Add watermark gap information into SS UI page

[GitBox <gi...@apache.org>]

xuanyuanking commented on a change in pull request #30427:
URL: https://github.com/apache/spark/pull/30427#discussion_r528546502



##########
File path: sql/core/src/main/scala/org/apache/spark/sql/streaming/ui/StreamingQueryStatisticsPage.scala
##########
@@ -126,6 +126,58 @@ private[ui] class StreamingQueryStatisticsPage(parent: StreamingQueryTab)
     <br />
   }
 
+  def generateWatermark(
+      query: StreamingQueryUIData,
+      minBatchTime: Long,
+      maxBatchTime: Long,
+      jsCollector: JsCollector): Seq[Node] = {
+    // This is made sure on caller side but put it here to be defensive
+    require(query.lastProgress != null)
+    if (query.lastProgress.eventTime.containsKey("watermark")) {
+      val watermarkData = query.recentProgress.flatMap { p =>
+        val batchTimestamp = parseProgressTimestamp(p.timestamp)
+        val watermarkValue = parseProgressTimestamp(p.eventTime.get("watermark"))
+        if (watermarkValue > 0L) {
+          // seconds
+          Some((batchTimestamp, ((batchTimestamp - watermarkValue) / 1000.0)))

Review comment:
       Fully agree with `knowing the gap between actual wall clock and watermark looks more useful than the absolute value.` and thanks for the super useful watermark info!
   
   I only have one concern same with @viirya https://github.com/apache/spark/pull/30427#issuecomment-730852396. Maybe we can address both scenarios(event time is/isn't close to clock time) by using the max event time received in this batch? I mean:
   ```
            if (watermarkValue > 0L) {
              // seconds
   -          Some((batchTimestamp, ((batchTimestamp - watermarkValue) / 1000.0)))
   +          val maxEventTime = parseProgressTimestamp(p.eventTime.get("max"))
   +          Some((batchTimestamp, (maxEventTime - watermarkValue) / 1000.0))
            } else {
              None
            }
   ```
   
   




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