Github user koeninger commented on a diff in the pull request:
https://github.com/apache/spark/pull/15820#discussion_r87130059
--- Diff:
external/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/CachedKafkaConsumer.scala
---
@@ -83,6 +86,113 @@ private[kafka010] case class CachedKafkaConsumer
private(
record
}
+ @tailrec
+ final def getAndIgnoreLostData(
+ offset: Long,
+ untilOffset: Long,
+ pollTimeoutMs: Long): ConsumerRecord[Array[Byte], Array[Byte]] = {
+ // scalastyle:off
+ // When `failOnDataLoss` is `false`, we need to handle the following
cases (note: untilOffset and latestOffset are exclusive):
+ // 1. Some data are aged out, and `offset < beginningOffset <=
untilOffset - 1 <= latestOffset - 1`
+ // Seek to the beginningOffset and fetch the data.
+ // 2. Some data are aged out, and `offset <= untilOffset - 1 <
beginningOffset`.
+ // There is nothing to fetch, return null.
+ // 3. The topic is deleted.
+ // There is nothing to fetch, return null.
+ // 4. The topic is deleted and recreated, and `beginningOffset <=
offset <= untilOffset - 1 <= latestOffset - 1`.
+ // We cannot detect this case. We can still fetch data like
nothing happens.
+ // 5. The topic is deleted and recreated, and `beginningOffset <=
offset < latestOffset - 1 < untilOffset - 1`.
+ // Same as 4.
+ // 6. The topic is deleted and recreated, and `beginningOffset <=
latestOffset - 1 < offset <= untilOffset - 1`.
+ // There is nothing to fetch, return null.
+ // 7. The topic is deleted and recreated, and `offset <
beginningOffset <= untilOffset - 1`.
+ // Same as 1.
+ // 8. The topic is deleted and recreated, and `offset <= untilOffset -
1 < beginningOffset`.
+ // There is nothing to fetch, return null.
+ // scalastyle:on
+ if (offset >= untilOffset) {
+ // Case 2 or 8
+ // We seek to beginningOffset but beginningOffset >= untilOffset
+ reset()
+ return null
+ }
+
+ logDebug(s"Get $groupId $topicPartition nextOffset
$nextOffsetInFetchedData requested $offset")
+ var outOfOffset = false
+ if (offset != nextOffsetInFetchedData) {
+ logInfo(s"Initial fetch for $topicPartition $offset")
+ seek(offset)
+ try {
+ poll(pollTimeoutMs)
+ } catch {
+ case e: OffsetOutOfRangeException =>
+ logWarning(s"Cannot fetch offset $offset, try to recover from
the beginning offset", e)
+ outOfOffset = true
+ }
+ } else if (!fetchedData.hasNext()) {
+ // The last pre-fetched data has been drained.
+ seek(offset)
+ try {
+ poll(pollTimeoutMs)
+ } catch {
+ case e: OffsetOutOfRangeException =>
+ logWarning(s"Cannot fetch offset $offset, try to recover from
the beginning offset", e)
+ outOfOffset = true
+ }
+ }
+ if (outOfOffset) {
+ val beginningOffset = getBeginningOffset()
+ if (beginningOffset <= offset) {
+ val latestOffset = getLatestOffset()
+ if (latestOffset <= offset) {
+ // Case 3 or 6
+ logWarning(s"Offset ${offset} is later than the latest offset
$latestOffset. " +
+ s"Skipped [$offset, $untilOffset)")
+ reset()
+ return null
+ } else {
+ // Case 4 or 5
+ getAndIgnoreLostData(offset, untilOffset, pollTimeoutMs)
--- End diff --
- Why isn't this an early return?
- Unless I'm misreading, this is a recursive call without changing the
arguments. Why is it guaranteed to terminate?
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