[jira] [Resolved] (HBASE-25460) Expose drainingServers as cluster metric

["Viraj Jasani (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-25460?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Viraj Jasani resolved HBASE-25460.
----------------------------------
    Fix Version/s: 2.4.2
                   2.3.5
                   2.2.7
     Hadoop Flags: Reviewed
       Resolution: Fixed

Thanks for the contribution [~rkrahul324].

> 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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