Github user srdo commented on a diff in the pull request:
https://github.com/apache/storm/pull/1679#discussion_r87022720
--- Diff:
external/storm-kafka-client/src/main/java/org/apache/storm/kafka/spout/KafkaSpout.java
---
@@ -479,16 +487,17 @@ public OffsetAndMetadata findNextCommitOffset() {
KafkaSpoutMessageId nextCommitMsg = null; // this is a
convenience variable to make it faster to create OffsetAndMetadata
for (KafkaSpoutMessageId currAckedMsg : ackedMsgs) { //
complexity is that of a linear scan on a TreeMap
- if ((currOffset = currAckedMsg.offset()) ==
initialFetchOffset || currOffset == nextCommitOffset + 1) { // found
the next offset to commit
+ if ((currOffset = currAckedMsg.offset()) ==
nextCommitOffset + 1) { // found the next offset to commit
found = true;
nextCommitMsg = currAckedMsg;
nextCommitOffset = currOffset;
} else if (currAckedMsg.offset() > nextCommitOffset + 1) {
// offset found is not continuous to the offsets listed to go in the next
commit, so stop search
LOG.debug("topic-partition [{}] has non-continuous
offset [{}]. It will be processed in a subsequent batch.", tp, currOffset);
break;
} else {
- LOG.debug("topic-partition [{}] has unexpected offset
[{}].", tp, currOffset);
- break;
+ //Received a redundant ack. Ignore and continue
processing.
--- End diff --
It can also happen if the Kafka cluster has unclean leader election
enabled. In that case, the log end offset in Kafka may become smaller than the
last offset the spout committed. It's a weird edge case, since most people
probably don't need to have at least once in Storm while allowing message loss
in Kafka. Bit of a newbie trap though, since unclean leader election is enabled
by default in Kafka.
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