Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/17219#discussion_r106746638
--- 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) {
--- End diff --
The above match-case, and this if statement essentially are the same
semantic conditions - both will be true or both will be false. So might as well
merge these two into a single if condition.
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