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https://issues.apache.org/jira/browse/HBASE-26147?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17389031#comment-17389031
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Bryan Beaudreault commented on HBASE-26147:
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There is probably more work we could do to make dry run even more useful in the
future, for example we could output what regions would have moved. I've been
using dry run internally for a while and honestly knowing the moves is not
super useful, especially in large clusters where a balance could mean hundreds
of moves. What _would_ probably be useful would be to print the full cost
breakdown of the chosen plan, or the full cost breakdown of the
best-but-not-chosen plan in the case where no plan was good enough. That would
be useful even in normal mode honestly, so I would prefer to make those sorts
of improvements in a separate issue. Just having the ability to run in dry run
mode is a great first step.
> 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
>
> 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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