[GitHub] incubator-trafodion pull request #1146: [TRAFODION-2661] Improve MDAM costin...

[DaveBirdsall <gi...@git.apache.org>]

GitHub user DaveBirdsall opened a pull request:

    https://github.com/apache/incubator-trafodion/pull/1146

    [TRAFODION-2661] Improve MDAM costing for RangeSpecs

    JIRA TRAFODION-1641 fixed an issue with MDAM costing, where MDAM costing was not accounting for the cost of recursion. That is, it was not accounting for the accumulated costs of probes as we recurse through a set of key columns. When analyzing that JIRA, I uncovered an issue with RangeSpec costing which I partially fixed.
    
    JIRA TRAFODION-2655 tuned the above fix further, increasing the weight of the cost of accumulated probes. So for plans lacking RangeSpecs, or plans whose RangeSpecs lack ORs, MDAM costing should now be doing a much better job of picking prefixes when it should.
    
    This fix addresses the last bit of the problem by addressing RangeSpecs. There was some code that was forcing MDAM plans to traverse all key columns when a RangeSpec containing an OR was present. I have simply deleted that code.
    
    I do not know why that code was originally there. It does predate the fixes noted above. I will speculate that before that change, we were picking MDAM in some cases where we should not, and adding that bit of code increased the total cost of MDAM to such a point that we no longer did.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/DaveBirdsall/incubator-trafodion Trafodion2661

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/incubator-trafodion/pull/1146.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #1146
    
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[GitHub] incubator-trafodion pull request #1146: [TRAFODION-2661] Improve MDAM costin...

[asfgit <gi...@git.apache.org>]

Github user asfgit closed the pull request at:

    https://github.com/apache/incubator-trafodion/pull/1146


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