Github user koeninger commented on a diff in the pull request: https://github.com/apache/spark/pull/15820#discussion_r87129817 --- 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) --- End diff -- I don't think it's necessary to seek every time the fetched data is empty, in normal operation the poll should return the next offset, right?
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