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https://issues.apache.org/jira/browse/HBASE-615?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12599225#action_12599225
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Jim Kellerman commented on HBASE-615:
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Well now it oscillates moving three regions around. There are 40 regions
including root and meta, 4 region servers, but the master refuses to give more
regions to the region server hosting the meta region. It has 4 regions and the
rest have 11, 12 or 13
> Region balancer oscillates during cluster startup
> -------------------------------------------------
>
> Key: HBASE-615
> URL: https://issues.apache.org/jira/browse/HBASE-615
> Project: Hadoop HBase
> Issue Type: Bug
> Components: master
> Affects Versions: 0.2.0
> Reporter: Jim Kellerman
> Assignee: Bryan Duxbury
> Fix For: 0.2.0
>
> Attachments: 615-lite.patch
>
>
> When starting a cluster with four region servers and a large table (49
> regions) (+root +meta) = 51 total regions, the region balancer oscillates for
> a very long time and does not seem to reach a steady state.
> Additionally, for whatever reason, it seems reluctant to assign regions to
> the first of four region servers, which may be the root cause. In my test,
> the first server had 10 regions assigned, the second and fourth had 13
> regions assigned, and the master would continually assign and deassign 2
> regions to the third server, which oscillated between 13 and 15 regions. If
> it assigned the two fluctuating regions to the first server, it would achieve
> the best balance possible: 12, 13, 13, 13.
> After 20 minutes, it had not stopped oscillating. An application trying to
> work against this cluster would run very slowly as it would be continually
> re-finding the two regions in flux.
> When the table was being created, regions were nicely balanced. On restart,
> however, it just would not settle down.
> Perhaps the balancer should set a target number of regions for each server
> which when the server achieved +/- 1 regions, the rebalancer would not try to
> change unless the number of regions changed.
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