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Date: Tue, 18 Mar 2014 20:33:48 +0000 (UTC)
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Subject: [jira] [Commented] (ACCUMULO-2488) Concurrent randomwalk balance
 check needs refinement
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    [ https://issues.apache.org/jira/browse/ACCUMULO-2488?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13939733#comment-13939733 ] 

ASF subversion and git services commented on ACCUMULO-2488:
-----------------------------------------------------------

Commit a4174248a96cadcc79a9de4015c90c6618a96418 in accumulo's branch refs/heads/1.5.2-SNAPSHOT from [~bhavanki]
[ https://git-wip-us.apache.org/repos/asf?p=accumulo.git;h=a417424 ]

ACCUMULO-2488 Change criteria for unbalanced servers in concurrent randomwalk

The Concurrent randomwalk test used to consider servers unbalanced if any server's
tablet count differed from the cluster average by more than a fifth of the average or
by one, whichever was larger. This would cause failures under typical balancings from
the default balancer.

This commit changes the criterion for an unbalanced server to be double the standard
deviation from the cluster average.


> Concurrent randomwalk balance check needs refinement
> ----------------------------------------------------
>
>                 Key: ACCUMULO-2488
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2488
>             Project: Accumulo
>          Issue Type: Test
>          Components: test
>    Affects Versions: 1.4.4
>            Reporter: Bill Havanki
>            Assignee: Bill Havanki
>            Priority: Minor
>              Labels: randomwalk, test
>             Fix For: 1.4.5, 1.5.2, 1.6.0
>
>
> The check for balanced tablets in the randomwalk Concurrent test too easily fails.
> Here is a real-life example from the test for the number of tablets across five tablet servers: 2, 5, 2, 2, 3. (An old unrelated table plays into these totals.) This produces a mean of 2.8. The cluster is considered unbalanced by the test when any server's count differs from the mean by the larger of 1 or the mean divided by 5. In this case, 2.8/5 is less than 1, so the second tablet server fails since it has more than 3.8 tablets. Even a 4 would fail.
> Part of the problem in this particular case is that there are so few tablets, and so few tablet servers. The cluster also seems happy to leave these counts as is, as I continue to check it, so the test's definition of unbalanced is too narrow.
> The test needs to be refined to detect unbalanced conditions with a statistically decent calculation.


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