jackjlli commented on issue #4972: Changing the rebalance strategy from Crush to AutoRebalance for contr… URL: https://github.com/apache/incubator-pinot/pull/4972#issuecomment-573472545 Affinity is needed when controller's workload is distributed to multiple controllers. E.g. suppose the leader of Partition X is host_1. After restarting host_1, we don't want the leader of partition X gets changed to other controller hosts after host_1 has been fully restarted; we want host_1 to always be the leader of Partition X. This can reduce the change of leadership change in the whole Pinot cluster. And crushED algorithm provides us this guarantee: http://helix.apache.org/0.8.4-docs/design_crushed.html 0.9.2 will also touch that exception, but it only prints a one-line message instead of the whole stack trace. Thus, the log will be clean. And the message will not longer appear after the first controller is fully prepared. The goal of leadControllerResource is to make sure there is at most 1 host in Master state within any partitions. OnlineOffline cannot guarantee that. E.g. if OnlineOffline state model is used, when a host gets restarted, it's possible that a state transition from offline to online gets triggered before the state transition from online to offline does, which leads to a scenario that there are two hosts in Online state, which is harmful to realtime segment completion.
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