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https://issues.apache.org/jira/browse/HBASE-25460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17295240#comment-17295240
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Anoop Sam John commented on HBASE-25460:
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Release Notes pls
> Expose drainingServers as cluster metric
> ----------------------------------------
>
> Key: HBASE-25460
> URL: https://issues.apache.org/jira/browse/HBASE-25460
> Project: HBase
> Issue Type: New Feature
> Components: metrics
> Affects Versions: 1.6.0, 2.4.0
> Reporter: Viraj Jasani
> Assignee: Rahul Kumar
> Priority: Major
> Fix For: 3.0.0-alpha-1, 1.7.0, 2.2.7, 2.5.0, 2.3.5, 2.4.2
>
>
> Due to some reason, we had significantly high number of servers put in
> decommissioned mode and for significant time, they continued being in the
> same state serving no regions at all. This put heavy load on rest of live
> servers and it was too late before one could recognize the issues with
> improper balancing of the cluster. And as expected, balancing such cluster
> with/without *runMaxSteps* can bring up sudden spike of RITs in proportion to
> the degree of imbalanced regions in the cluster.
> Although running into such situation is rare, we can take some precautions by
> exposing metric. We should expose list of draining RegionServers as jmx
> metrics just like we expose _*liveRegionServers*_ and _*deadRegionServers*_.
> Such metric can help configure alerts with threshold on % of total RS that
> are allowed to go in draining mode (e.g during rolling upgrades) in any
> circumstances.
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