Current state: Under Discussion
Discussion thread: here
JIRA: here
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
One of MM2's main features is syncing consumer group offset between clusters. This feature relies on two separate connectors
MirrorSourceConnector : this connector stores the translation of the new recored's offset on target cluster in offset_syncs internal topic after mirroring the record itself. This translation is done at commit method since 3.5 where commit() API stores the offsets in the source system, up to the offsets that have been returned by poll() . The implementation of this API should block until the commit is complete. See [KAFKA-14610](https://issues.apache.org/jira/browse/KAFKA-14610) for more details.MirrorCheckpointConnector : this connector uses the new record offsets from offset_syncs and update checkpoints and __consumer_offsets topics. This can be controlled by emit.checkpoints.enabled and sync.group.offsets.enabled For use-cases where customers only run MM2 for replicating between clusters without the need for moving the consumer group offsets by running only MirrorSourceConnector. They still left with part#1 of this feature which add cost to the progress of their replication. The only workaround reducing the latency cost is by increasing offset.lag.max to INT_MAX which will result that the offset will never going to be queued for offset sync (Check `PartitionState::update` for details on how MM2 decided if it should emit an offset sync or not) however this doesn't eliminate the cost of creating an internal topic.
This KIP propose that we add a new config for MirrorSourceConnector to control enabling the offsets translation between clusters for replicated topics.
| Properties | Default | Description |
|---|---|---|
emit.offset-syncs.enabled | true | Whether to store the new offset of the replicated records in offset-syncs topic or not. MirrorCheckpointConnector will fail to start if emit.checkpoints.enabled and/or sync.group.offsets.enabled are enabled while |
emit.checkpoints.enabled and emit.heartbeat.enabled this KIP will add emit.offset-syncs.enabled. The config default value will be true to keep the current implementation.offset-syncs topic will not be created if emit.offset-syncs.enabled set to false
logic to publish offset syncs in commit() will not be executed if emit.offset-syncs.enabled set to false
MirrorCheckpointConnector validation will fail at start if emit.offset-syncs.enabled disabled while emit.checkpoints.enabled and/or sync.group.offsets.enabled are enabled.
emit.offset-syncs.enabled is set to true by default so any existing use-cases or use-cases that run this feature will do nothing. Only use-case that wish to fully disable this feature will need to set emit.offset-syncs.enabled to false.
emit.checkpoints.enabled and sync.group.offsets.enabled and assume that if both are disabled then this feature needs to be fully disabled. I didn't want to relay on MirrorCheckpointConnector configs to configure MirrorSourceConnector. And this might impact customers who enabled MirrorSourceConnector with intention to run MirrorCheckpointConnector later in the future