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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