Gabriella Lotz created KUDU-3802:
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Summary: Add cluster leader-skew gauge
Key: KUDU-3802
URL: https://issues.apache.org/jira/browse/KUDU-3802
Project: Kudu
Issue Type: Sub-task
Reporter: Gabriella Lotz
The counters on the auto-rebalancer and the ones added under KUDU-3791 for the
auto-leader-rebalancer report activity: how many moves were scheduled, how many
rounds completed. They don't report whether the cluster is currently skewed.
The replica side already has this: `cluster_replica_skew` at `ts_manager.cc:55`
is a function gauge that returns the difference between the tserver with the
most replicas and the tserver with the fewest.
Add a matching `cluster_leader_skew` gauge: max minus min leader count across
live tservers. The leader rebalancer already computes this per-round in
`RunLeaderRebalancer`, so the gauge can share that state or recompute on scrape.
This gives operators a "does the cluster need rebalancing right now" signal to
sit alongside the "is the rebalancer doing anything" signals from the counters.
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