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From "Bryan Duxbury (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HBASE-615) Region balancer oscillates during cluster startup
Date Thu, 19 Jun 2008 15:07:45 GMT

     [ https://issues.apache.org/jira/browse/HBASE-615?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Bryan Duxbury updated HBASE-615:
--------------------------------

    Attachment: 615-v2.patch

Here's a patch that removes the number of requests from the load considerations. It passes
unit tests (except TestMetaUtils, which times out, but appears unrelated). 

Jim, can you test this on your cluster and see if it reduces oscillation?

> 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, 615-v2.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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