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The set of shutting down tservers was causing system fate operations to have to run on the primary manager because this was an in memory set. This caused fate to have different code paths to user vs system fate, this in turn caused problems when trying to distribute compaction coordination. To fix this problem moved the set from an in memory set to a set in zookeeper. The set is managed by fate operations which simplifies the existing code. Only fate operations add and remove from the set and fate keys are used to ensure only one fate operation runs at a time for a tserver instance. The previous in memory set had a lot of code to try to keep it in sync with reality, that is all gone now. There were many bugs with this code in the past. After this change is made fate can be simplified in a follow on commit to remove all specialization for the primary manager. Also the monitor can now directly access this set instead of making an RPC to the manager, will open a follow on issue for this.
After this change meta fate and user fate are both treated mostly the same in the managers. One difference is in assignment, the entire meta fate range is assigned to a single manager. User fate is spread across all managers. But both are assigned out by the primary manager using the same RPCs now. The primary manager used to directly start a meta fate instance. Was able to remove the extension of FateEnv from the manager class in this change, that caused a ripple of test changes. But now there are no longer two different implementations of FateEnv
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Opened this as a draft PR, its a follow on to #6224 and currently includes commits from that PR as it builds on it.
This is part of a sequence of changes needed for #6217