Github user zsxwing commented on a diff in the pull request:
https://github.com/apache/spark/pull/12797#discussion_r61774375
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/TriggerExecutor.scala
---
@@ -65,8 +65,22 @@ case class ProcessingTimeExecutor(processingTime:
ProcessingTime, clock: Clock =
s"${intervalMs} milliseconds, but spent ${realElapsedTimeMs}
milliseconds")
}
- /** Return the next multiple of intervalMs */
+ /** Return the next multiple of intervalMs
+ *
+ * e.g. for intervalMs = 100
+ * nextBatchTime(0) = 100
+ * nextBatchTime(1) = 100
+ * ...
+ * nextBatchTime(99) = 100
+ * nextBatchTime(100) = 200
+ * nextBatchTime(101) = 200
+ * ...
+ * nextBatchTime(199) = 200
+ * nextBatchTime(200) = 300
+ *
+ * Note, this way, we'll get nextBatchTime(nextBatchTime(0)) = 200,
rather than = 0
+ * */
def nextBatchTime(now: Long): Long = {
- (now - 1) / intervalMs * intervalMs + intervalMs
+ now / intervalMs * intervalMs + intervalMs
--- End diff --
When I wrote this method, I was trying to deal with one case: If a batch
takes exactly `intervalMs`, we should run the next batch at once instead of
sleeping `intervalMs`. This changes will break it.
However, I forgot to handle the case that a batch takes 0ms. How about
changing [this
line](https://github.com/apache/spark/blob/0513c3ac93e0a25d6eedbafe6c0561e71c92880a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/TriggerExecutor.scala#L53)
to:
```Scala
if (batchElapsedTimeMs == 0) {
clock.waitTillTime(intervalMs)
} else {
clock.waitTillTime(nextBatchTime(batchEndTimeMs))
}
```
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