Github user zsxwing commented on a diff in the pull request:
https://github.com/apache/spark/pull/14553#discussion_r83965244
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala
---
@@ -336,17 +342,27 @@ class StreamExecution(
}
if (hasNewData) {
reportTimeTaken(OFFSET_WAL_WRITE_LATENCY) {
- assert(
- offsetLog.add(currentBatchId,
availableOffsets.toCompositeOffset(sources)),
+ assert(offsetLog.add(currentBatchId,
availableOffsets.toCompositeOffset(sources)),
s"Concurrent update to the log. Multiple streaming jobs detected
for $currentBatchId")
logInfo(s"Committed offsets for batch $currentBatchId.")
+ // Now that we've updated the scheduler's persistent checkpoint,
it is safe for the
+ // sources to discard data from *before* the previous batch.
+ // The scheduler might still request the previous batch from a
source in some cases
+ // if a crash and recovery occured.
+ val prevBatchOff = offsetLog.get(currentBatchId - 2)
--- End diff --
Can we just commit `currentBatchId - 1`? In which case, it will fail?
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