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From "Bill Havanki (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (ACCUMULO-2488) Concurrent randomwalk balance check needs refinement
Date Tue, 18 Mar 2014 20:37:45 GMT

     [ https://issues.apache.org/jira/browse/ACCUMULO-2488?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Bill Havanki updated ACCUMULO-2488:
-----------------------------------

    Resolution: Fixed
        Status: Resolved  (was: Patch Available)

I've committed the adjustment as reviewed. ACCUMULO-2494 is about updating the standard deviation
computation in {{o.a.a.core.util.Stat}}. Depending on how that turns out, the updated capability
could be reused here, replacing the naive method I implemented. I'd be fine with either reopening
this ticket to put in that change or having it done under ACCUMULO-2494.

> 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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