fvaleri commented on code in PR #14121:
URL: https://github.com/apache/kafka/pull/14121#discussion_r1277749103
##########
examples/src/main/java/kafka/examples/Consumer.java:
##########
@@ -157,9 +157,4 @@ public void onPartitionsRevoked(Collection<TopicPartition>
partitions) {
public void onPartitionsAssigned(Collection<TopicPartition> partitions) {
Utils.printOut("Assigned partitions: %s", partitions);
}
-
- @Override
- public void onPartitionsLost(Collection<TopicPartition> partitions) {
- Utils.printOut("Lost partitions: %s", partitions);
Review Comment:
Hi @dajac, the default implementation of onPartitionsLost calls
onPartitionsRevoked so that any cleanup logic can be executed (i.e. commit
pending offsets before losing the partition ownership). This also means that
"revoked" is logged instead of "lost".
https://github.com/fvaleri/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerRebalanceListener.java#L197-L199
For this reason, I thought we could simply use the default implementation
without overriding, but now I see that it is too late to save the offsets when
onPartitionsLost is called, since these partitions are probably owned by other
consumers already.
From the javadoc we have:
```sh
public void onPartitionsLost(Collection<TopicPartition> partitions) {
// do not need to save the offsets since these partitions are probably
owned by other consumers already
}
```
The default onPartitionsLost implementation is there to cover the case where
partitions are reassigned before we have a chance to revoke them gracefully
(i.e. in case of session timeout). Maybe we can leave the override adding an
appropriate comment. Wdyt?
Something like:
```sh
// this is called when partitions are reassigned before we had a chance to
revoke them gracefully
// we can't commit pending offsets because these partitions are probably
owned by other consumers already
// nevertheless, we may need to do some other cleanup
```
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