Minor Description
Throughout the process of a ZK to KRaft migration, the operator has the choice to revert back to ZK mode. Once this is done, there will be a copy of the metadata log on each broker in the cluster.
In order to re-attempt the migration in the future, this metadata log needs to be deleted. This can be pretty burdensome to the operator for large clusters, especially since the log deletion must be done while the broker is offline.
To improve this, we can automatically delete any metadata log present during startup of a ZK broker. In general, it is always safe to remove the metadata log from a KRaft or migrating ZK broker. The main impact is that this will delay the time it takes for the broker to be unfenced by the controller since it has to re-replicate the log. In the case of hybrid mode ZK brokers, there will be a delay in them receiving their first UpdateMetadataRequest from the controller (for the same reason – delay in getting unfenced).
The delayed startup should not affect the performance of the cluster, though it would increase the overall time required to do a rolling restart of the cluster.
Once a broker restarts as KRaft, we will stop doing this automatic deletion.