Github user koeninger commented on a diff in the pull request:
https://github.com/apache/spark/pull/15820#discussion_r87439798
--- Diff:
external/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/CachedKafkaConsumer.scala
---
@@ -83,6 +86,129 @@ private[kafka010] case class CachedKafkaConsumer
private(
record
}
+ /**
+ * Get the record at the `offset`. If it doesn't exist, try to get the
earliest record in
+ * `[offset, untilOffset)`.
+ */
+ 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
+ require(offset < untilOffset, s"offset: $offset, untilOffset:
$untilOffset")
+ logDebug(s"Get $groupId $topicPartition nextOffset
$nextOffsetInFetchedData requested $offset")
+ try {
+ if (offset != nextOffsetInFetchedData) {
+ logInfo(s"Initial fetch for $topicPartition $offset")
+ seek(offset)
+ poll(pollTimeoutMs)
+ } else if (!fetchedData.hasNext()) {
+ // The last pre-fetched data has been drained.
+ poll(pollTimeoutMs)
+ }
+ getRecordFromFetchedData(offset, untilOffset)
+ } catch {
+ case e: OffsetOutOfRangeException =>
+ logWarning(s"Cannot fetch offset $offset, try to recover from the
beginning offset", e)
+ advanceToBeginningOffsetAndFetch(offset, untilOffset,
pollTimeoutMs)
+ }
+ }
+
+ /**
+ * Try to advance to the beginning offset and fetch again.
`beginningOffset` should be in
+ * `[offset, untilOffset]`. If not, it will try to fetch `offset` again
if it's in
+ * `[beginningOffset, latestOffset)`. Otherwise, it will return null and
reset the pre-fetched
+ * data.
+ */
+ private def advanceToBeginningOffsetAndFetch(
+ offset: Long,
+ untilOffset: Long,
+ pollTimeoutMs: Long): ConsumerRecord[Array[Byte], Array[Byte]] = {
+ val beginningOffset = getBeginningOffset()
+ if (beginningOffset <= offset) {
+ val latestOffset = getLatestOffset()
+ if (latestOffset <= offset) {
+ // beginningOffset <= latestOffset - 1 < offset <= untilOffset - 1
+ logWarning(s"Offset ${offset} is later than the latest offset
$latestOffset. " +
+ s"Skipped [$offset, $untilOffset)")
+ reset()
+ null
+ } else {
+ // beginningOffset <= offset <= min(latestOffset - 1, untilOffset
- 1)
+ getAndIgnoreLostData(offset, untilOffset, pollTimeoutMs)
+ }
+ } else {
+ if (beginningOffset >= untilOffset) {
+ // offset <= untilOffset - 1 < beginningOffset
+ logWarning(s"Buffer miss for $groupId $topicPartition [$offset,
$untilOffset)")
+ reset()
+ null
+ } else {
+ // offset < beginningOffset <= untilOffset - 1
+ logWarning(s"Buffer miss for $groupId $topicPartition [$offset,
$beginningOffset)")
+ getAndIgnoreLostData(beginningOffset, untilOffset, pollTimeoutMs)
+ }
+ }
+ }
+
+ /**
+ * Get the earliest record in [offset, untilOffset) from the fetched
data. If there is no such
+ * record, returns null. Must be called after `poll`.
+ */
+ private def getRecordFromFetchedData(
+ offset: Long,
+ untilOffset: Long): ConsumerRecord[Array[Byte], Array[Byte]] = {
+ if (!fetchedData.hasNext()) {
+ // We cannot fetch anything after `poll`. Two possible cases:
+ // - `beginningOffset` is `offset` but there is nothing for
`beginningOffset` right now.
+ // - Cannot fetch any date before timeout.
--- End diff --
As a user, I'm not sure that setting failOnDataLoss=false would make me
know that a timeout would cause me to miss data in my spark job (that might
otherwise still be in kafka)
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