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From "Bill Havanki (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ACCUMULO-2488) Concurrent randomwalk balance check needs refinement
Date Mon, 17 Mar 2014 21:12:42 GMT
Bill Havanki created ACCUMULO-2488:
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             Summary: 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


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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