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https://issues.apache.org/jira/browse/ACCUMULO-2494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13940948#comment-13940948
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Mike Drob commented on ACCUMULO-2494:
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I should have been more clear.
{quote}
I have seen multiple times in the past where small seemingly innocuous changes
for minor bugs have introduced critical bugs. In this case TabletServer uses
the Stat class, but does not use the std deviation. The risk is a small
possibility of introducing a new critical bug in tserver if the change breaks
Stat in some strange new way. The benefit of the change is that informational
output from a few test may be better.
{quote}
Based on this comment, I do not understand which version you would support
including the new implementation of Stat in. I also do not understand if you
would support fixing stdev in older versions while leaving everything else the
same. FWIW, my implementation and the commons-math implementation were the same
(theirs was a bit more general and better documented, but otherwise identical).
The reason I asked for clarification is that I cannot tell if you are -1 or -0
on including the full change in 1.5.x.
{quote}
Something else that would cause problems would be if the Apache library stored
all of the data you were computing stats for. I assume it does not do this,
but would have to inspect the code to be sure.
{quote}
It does not store the data, so this is not an issue.
> Stat calculation of STDEV may be inaccurate
> -------------------------------------------
>
> Key: ACCUMULO-2494
> URL: https://issues.apache.org/jira/browse/ACCUMULO-2494
> Project: Accumulo
> Issue Type: Bug
> Components: client
> Reporter: Mike Drob
>
> The math is sound, but it is susceptible to rounding errors. We should
> address that.
> See http://www.strchr.com/standard_deviation_in_one_pass and
> http://www.cs.berkeley.edu/~mhoemmen/cs194/Tutorials/variance.pdf
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