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https://issues.apache.org/jira/browse/HBASE-14309?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ted Yu updated HBASE-14309:
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Release Note:
This issue adds boolean parameter, force, to 'balancer' command so that admin
can force region balancing even when there is region (other than hbase:meta) in
transition - assuming RIT being transient.
WARNING: For experts only. Forcing a balance may do more damage than repair
when assignment is confused
> Allow load balancer to operate when there is region in transition by adding
> force flag
> --------------------------------------------------------------------------------------
>
> Key: HBASE-14309
> URL: https://issues.apache.org/jira/browse/HBASE-14309
> Project: HBase
> Issue Type: Improvement
> Reporter: Ted Yu
> Assignee: Ted Yu
> Fix For: 2.0.0, 1.3.0
>
> Attachments: 14309-branch-1.1.txt, 14309-v1.txt, 14309-v2.txt,
> 14309-v3.txt, 14309-v4.txt, 14309-v5-branch-1.txt, 14309-v5.txt,
> 14309-v5.txt, 14309-v6.txt, 14309-v7.txt
>
>
> This issue adds boolean parameter, force, to 'balancer' command so that admin
> can force region balancing even when there is region in transition - assuming
> RIT being transient.
> This enhancement was requested by some customer.
> The assumption of this change is that the operator has run hbck and has a
> reasonable idea why regions are stuck in transition before using the force
> flag.
> There was a recent event at the customer where a cluster ended up with a
> small number of regionservers hosting most of the regions on the cluster (one
> regionserver had 50% of the roughly 20,000 regions). The balancer couldn't be
> run due to the small number of regions that were stuck in transition. The
> admin ended up killing the regionservers so that reassignment would yield a
> more equitable distribution of the regions.
> On a different cluster, there was a single store file that had corrupt HDFS
> blocks (the SSDs on the cluster were known to lose data). However, since this
> single region (out of 10s of 1000s of regions on this cluster) was stuck in
> transition, the balancer couldn't run.
> While the state keeping in HBase isn't so good yet that the admin can kick
> off the balancer automatically in such scenarios knowing when it is safe to
> do so and when it is not, having this option available for the operator to
> use as he / she sees fit seems prudent.
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