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[release-1.0] Document Kafka Broker commit offset interval (#4560) 

* Document Kafka Broker commit offset interval

Signed-off-by: Pierangelo Di Pilato <pdipilat@redhat.com>

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Signed-off-by: Pierangelo Di Pilato <pdipilat@redhat.com>

Co-authored-by: Pierangelo Di Pilato <pdipilat@redhat.com>
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@ -224,6 +224,41 @@ kubectl create secret --namespace <namespace> generic <my_secret> \
_NOTE: `ca.crt` can be omitted to fallback to use system's root CA set._
## Consumer Offsets Commit Interval
Kafka consumers keep track of the last successfully sent events by committing offsets.
Knative Kafka Broker commits the offset every `auto.commit.interval.ms` milliseconds.
!!! note
To prevent negative impacts to performance, it is not recommended committing
offsets every time an event is successfully sent to a subscriber.
The interval can be changed by changing the `config-kafka-broker-data-plane` `ConfigMap`
in the `knative-eventing` namespace by modifying the parameter `auto.commit.interval.ms` as follows:
```yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: config-kafka-broker-data-plane
namespace: knative-eventing
data:
# Some configurations omitted ...
config-kafka-broker-consumer.properties: |
# Some configurations omitted ...
# Commit the offset every 5000 millisecods (5 seconds)
auto.commit.interval.ms=5000
```
!!! note
Knative Kafka Broker guarantees at least once delivery, which means that your applications may
receive duplicate events. A higher commit interval means that there is a higher probability of
receiving duplicate events, because when a Consumer restarts, it restarts from the last
committed offset.
## Kafka Producer and Consumer configurations
Knative exposes all available Kafka producer and consumer configurations that can be modified to suit your workloads.