Hi Ron, Thanks for drilling down on this. I think the KIP isn't really clear here, and the metadata caching section you quoted needs clarification.
The "hosting broker's latest registration" refers to the previous, not the current registration. The registrations are only compared by the controller, when handling the broker registration request. Suppose broker b1 hosts two partitions, t-1 and t-2, in two directories, d1 and d2. The broker is registered, and the metadata correlates the replicas to their respective directories. i.e. OnlineLogDirs=[d1,d2] and OfflineLogDirs=false The broker is then reconfigured to remove t-2 from log.dirs, and at startup, the registration request shows OnlineLogDirs=[d1] and OfflineLogDirs=false. The previous registration will only be replaced after a new successful registration, regardless of how quickly or how often b1 restarts. The controller compares the previous registration, and notices that one of the directories has been removed. So for any replica hosted in the broker that is assigned to that missing log directory, a logical metadata update takes place that assigned them to Uuid.OfflineDir, so Assignment.Directory is updated for t-2. This value is indicates that the replica is offline — I have updated the section you quoted to address this. Once the broker catches up with metadata, it will select the only configured log directory — d1 — for any partitions assigned to Uuid.OfflineDir, and update the assignment. Best, -- Igor
