As long as the consumer group is active, nothing will be deleted. That
is the reason why you get those incorrect alerts -- Kafka cannot know
that you stopped consuming from those topics. (That is what I tried to
explain -- seems I did a bad job...)
Changing the group.id is tricky because Kafka Streams uses it to
identify internal topic names (for repartiton and chagnelog topics), and
thus your app would start with newly created (and thus empty topics). --
You might want to restart the app with `auto.offset.reset = "earliest"`
and reprocess all available input to re-create state.
-Matthias
On 8/19/23 8:07 AM, Pushkar Deole wrote:
@matthias
what are the alternatives to get rid of this issue? When the lag starts
increasing, we have alerts configured on our monitoring system in Datadog
which starts sending alerts and alarms to reliability teams. I know in
kafka the inactive consumer group is cleared up after 7 days however not
sure if that is the case with topics that were consumed previously and not
consumed now.
Does creation of new consumer group (setting a different application.id) on
streams application an option here?
On Thu, Aug 17, 2023 at 7:03 AM Matthias J. Sax <mj...@apache.org> wrote:
Well, it's kinda expected behavior. It's a split brain problem.
In the end, you use the same `application.id / group.id` and thus the
committed offsets for the removed topics are still in
`__consumer_offsets` topics and associated with the consumer group.
If a tool inspects lags and compares the latest committed offsets to
end-offsets it looks for everything it finds in the `__consumer_offsets`
topics for the group in question -- the tool cannot know that you
changed the application and that is does not read from those topics any
longer (and thus does not commit any longer).
I am not sure from top of my head if you could do a manual cleanup for
the `application.id` and topics in question and delete the committed
offsets from the `__consumer_offsets` topic -- try to checkout `Admin`
client and/or the command line tools...
In know that it's possible to delete committed offsets for a consumer
group (if a group becomes inactive, the broker would also cleanup all
group metadata after a configurable timeout), but I am not sure if
that's for the entire consumer group (ie, all topic) or if you can do it
on a per-topic basis, too.
HTH,
-Matthias
On 8/16/23 2:11 AM, Pushkar Deole wrote:
Hi streams Dev community @matthias, @bruno
Any inputs on above issue? Is this a bug in the streams library wherein
the
input topic removed from streams processor topology, the underlying
consumer group still reporting lag against those?
On Wed, Aug 9, 2023 at 4:38 PM Pushkar Deole <pdeole2...@gmail.com>
wrote:
Hi All,
I have a streams application with 3 instances with application-id set to
applicationV1. The application uses processor API with reading from
source
topics, processing the data and writing to destination topic.
Currently it consumes from 6 source topics however we don't need to
process data any more from 2 of those topics so we removed 2 topics from
the source topics list. We have configured Datadog dashboard to report
and
alert on consumer lag so after removing the 2 source topics and
deploying
application, we started getting several alerts about consumer lag on
applicationV1 consumer group which is underlying consumer group of the
streams application. When we looked at the consumer group from
kafka-cli,
we could see that the consumer group is reporting lag against the topics
removed from source topic list which is reflecting as increasing lag on
Datadog monitoring.
Can someone advise if this is expected behavior? In my opinion, this is
not expected since streams application no more has those topics as part
of
source, it should not report lag on those.
