[jira] [Resolved] (HBASE-26147) Add dry run mode to hbase balancer

["Josh Elser (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-26147?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Josh Elser resolved HBASE-26147.
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    Resolution: Fixed

Thanks for the excellent work, Bryan. This really came together to be a great change. I took the liberty of writing some release notes – please feel free to update them as you see fit.

Thanks Duo, Nick, and everyone else who helped out in reviews.

My apologies that I botched application of the branch-2 PR (putting my own email address instead of Bryan's). I reverted my original commit and re-applied it with correct metadata. Sorry for sullying the commit log. 

> Add dry run mode to hbase balancer
> ----------------------------------
>
>                 Key: HBASE-26147
>                 URL: https://issues.apache.org/jira/browse/HBASE-26147
>             Project: HBase
>          Issue Type: Improvement
>          Components: Balancer, master
>            Reporter: Bryan Beaudreault
>            Assignee: Bryan Beaudreault
>            Priority: Major
>             Fix For: 2.5.0, 3.0.0-alpha-2
>
>
> It's often rather hard to know how the cost function changes you're making will affect the balance of the cluster, and currently the only way to know is to run it. If the cost decisions are not good, you may have just moved many regions towards a non-ideal balance. Region moves themselves are not free for clients, and the resulting balance may cause a regression.
> We should add a mode to the balancer so that it can be invoked without actually executing any plans. This will allow an administrator to iterate on their cost functions and used the balancer's logging to see how their changes would affect the cluster. 



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