Github user tdas commented on a diff in the pull request:

    https://github.com/apache/spark/pull/17219#discussion_r106744878
  
    --- Diff: 
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala
 ---
    @@ -373,22 +380,66 @@ class StreamExecution(
        *  - currentBatchId
        *  - committedOffsets
        *  - availableOffsets
    +   *  The basic structure of this method is as follows:
    +   *
    +   *  Identify (from the offset log) the offsets used to run the last batch
    +   *  IF a last batch exists THEN
    +   *    Set the next batch to that last batch
    +   *    Check the commit log to see which batch was committed last
    +   *    IF the last batch was committed THEN
    +   *      Call getBatch using the last batch start and end offsets
    +   *      Setup for a new batch i.e., start = last batch end, and identify 
new end
    +   *    DONE
    +   *  ELSE
    +   *    Identify a brand new batch
    +   *  DONE
        */
       private def populateStartOffsets(): Unit = {
         offsetLog.getLatest() match {
           case Some((batchId, nextOffsets)) =>
    -        logInfo(s"Resuming streaming query, starting with batch $batchId")
    -        currentBatchId = batchId
             availableOffsets = nextOffsets.toStreamProgress(sources)
             offsetSeqMetadata = 
nextOffsets.metadata.getOrElse(OffsetSeqMetadata())
    -        logDebug(s"Found possibly unprocessed offsets $availableOffsets " +
    -          s"at batch timestamp ${offsetSeqMetadata.batchTimestampMs}")
    -
    -        offsetLog.get(batchId - 1).foreach {
    -          case lastOffsets =>
    +        if (batchId > 0) {
    +          // We have committed at least one batch
    +          offsetLog.get(batchId - 1).foreach { lastOffsets =>
                 committedOffsets = lastOffsets.toStreamProgress(sources)
                 logDebug(s"Resuming with committed offsets: $committedOffsets")
    +          }
    +        }
    +        /* identify the current batch id: if commit log indicates we 
successfully processed the
    +         * latest batch id in the offset log, then we can safely move to 
the next batch
    +         * i.e., committedBatchId + 1
    +         */
    +        currentBatchId = commitLog.getLatest() match {
    +          case Some((committedBatchId, _))
    +            if batchId == committedBatchId => committedBatchId + 1
    +          case _ => batchId
    +        }
    +        if (batchId < currentBatchId) {
    +          /* The last batch was successfully committed, so we can safely 
process a
    +           * new next batch but first:
    +           * Make a call a call to getBatch using the offsets from 
previous batch.
    --- End diff --
    
    "a call" is present twice.


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