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From koeninger <...@git.apache.org>
Subject [GitHub] spark pull request #15820: [SPARK-18373][SS][Kafka]Make failOnDataLoss=false...
Date Thu, 10 Nov 2016 17:13:34 GMT
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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