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https://issues.apache.org/jira/browse/HBASE-3799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13021661#comment-13021661
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stack commented on HBASE-3799:
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A general comment on balancing (that probably fits better elsewhere than as a
comment on this issue) is that we need 'smoothing' of region move.... Yesterday
we brought a regionserver back online into a smallish cluster that was under
load and the balance run unloaded a bunch of regions all in the one go which
put a dent in the throughput; it'd be sweet if the balancer ran at an
appropriate 'rate'. When under load, it should move regions 'gently' rather
than all as a big bang (the decommission script will move a region at a time,
verifying it deployed in its new location before moving another... this can
take ages to complete but its proven minimally disruptive to loadings)
> Provide more accurate check for super underloaded region server in load
> balancer
> --------------------------------------------------------------------------------
>
> Key: HBASE-3799
> URL: https://issues.apache.org/jira/browse/HBASE-3799
> Project: HBase
> Issue Type: Bug
> Components: mapreduce
> Affects Versions: 0.90.2
> Reporter: Ted Yu
> Assignee: Ted Yu
>
> HBASE-3609 used simple check for region server which recently joined the
> cluster so that both young and old regions from other region servers are
> assigned to it.
> The check was too strict.
> 1 or more region may be assigned to this server before load balancer performs
> rebalancing.
> The next time balancer runs, it wouldn't treat this server as seriously
> underloaded correctly and assign a lot of young regions to it.
> We can use threshold over the number of regions to avoid such issue.
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