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Consumer group rebalancing may impact the performance of clients.  The rebalancing process may also sometimes take longer than expected. It would be good to have some metrics which provide visibility into how many rebalances are in progress.

Public

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Interface Additions and Changes

The group state name "AwaitingSync" is a bit confusing.  It is part of rebalancing, but it does not have "Rebalancing" in the name.  We propose renaming this state to "CompletingRebalance", to reflect the fact that it is the final part of the rebalancing operation.

Then we will add We should add new metrics identifying how many consumer groups are in each state.

• NumGroupsRebalancingNumGroupsPreparingRebalance: the number of consumer groups which are currently in the Rebalancing PreparingRebalance state.
  
• NumGroupsAwaitingSyncNumGroupsCompletingRebalance: the number of consumer groups which are currently in the AwaitingSync CompletingRebalance state.
• NumGroupsStable: the number of groups which are currently in the Stable state.
• NumGroupsDead: the number of groups which are currently in the Dead state.
• NumGroupsEmpty: the number of groups which are currently in the Empty state.

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