I was trying to expand our kafka cluster of 6 broker nodes to 12 broker nodes.
Before expansion, we had a single topic with 960 partitions and a replication factor of 3. So each node had 480 partitions. The size of data in each node was 3TB .
To do the expansion, I submitted a partition reassignment plan (see attached file for the current/new assignments). The plan was optimized to minimize data movement and be rack aware.
When I submitted the plan, it took approximately 3 hours for moving data from old to new nodes to complete. After that, it started deleting source partitions (I say this based on the number of file descriptors) and rebalancing leaders which has not been successful. Meanwhile, the heap usage in the controller node started to go up with a large slope (along with long GC times) and it took 5 hours for the controller to go out of memory and another controller started to have the same behaviour for another 4 hours. At this time the zookeeper ran out of disk and the service stopped.
To recover from this condition:
1) Removed zk logs to free up disk and restarted all 3 zk nodes
2) Deleted /kafka/admin/reassign_partitions node from zk
3) Had to do unclean restarts of kafka service on oom controller nodes which took 3 hours to complete . After this stage there was still 676 under replicated partitions.
4) Do a clean restart on all 12 broker nodes.
After step 4 , number of under replicated nodes went to 0.
So I was wondering if this memory footprint from controller is expected for 1k partitions ? Did we do sth wrong or it is a bug?
Attached are some resource usage graph during this 30 hours event and the reassignment plan. I'll try to add log files as well