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From "Bryan Duxbury (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-615) Region balancer oscillates during cluster startup
Date Wed, 18 Jun 2008 22:03:45 GMT

    [ https://issues.apache.org/jira/browse/HBASE-615?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12606110#action_12606110
] 

Bryan Duxbury commented on HBASE-615:
-------------------------------------

Should we just disable factoring in requests in a region server's load for the moment? It
might lead to a worse distribution of regions, but it might also make no difference, if on
average all regions are equally busy, which would be the case if you're running big time map/reduce
jobs. If you have hot rows/regions, then this could hurt you, but it's hard to say by how
much.

> 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
>            Priority: Blocker
>             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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