Github user koeninger commented on a diff in the pull request: https://github.com/apache/spark/pull/15820#discussion_r87438222 --- 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) --- End diff -- I'm clearer on why this terminates, but I think it's worth a comment, since it's a mutually recursive call without changing arguments.
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