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https://issues.apache.org/jira/browse/TRAFODION-2765?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16210260#comment-16210260
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ASF GitHub Bot commented on TRAFODION-2765:
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GitHub user DaveBirdsall opened a pull request:
https://github.com/apache/incubator-trafodion/pull/1269
Fix latent bug unmasked by JIRA TRAFODION-2765 fix
This fix comments out some code that now causes non-determinstic failures
in test compGeneral/TEST006. The essence of the bug is that queries against
tables lacking statistics would non-deterministically flip to MDAM. The
commented-out code contains several issues; rather than fixing them it seems
more efficient to simply continue with the MDAM costing code rewrite which is
occurring under JIRA TRAFODION-2645.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/DaveBirdsall/incubator-trafodion Trafodion2777
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/incubator-trafodion/pull/1269.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 #1269
----
commit 682c48e260d6bde50b13bf40567c9353e3b3dcda
Author: Dave Birdsall <[email protected]>
Date: 2017-10-18T21:45:04Z
Rework to address compGeneral/TEST006 failure
(cherry picked from commit 6320b901b6f123da9697dc8a898785168958dc10)
----
> MDAM is not considered when sometimes it should be
> --------------------------------------------------
>
> Key: TRAFODION-2765
> URL: https://issues.apache.org/jira/browse/TRAFODION-2765
> Project: Apache Trafodion
> Issue Type: Bug
> Components: sql-cmp
> Affects Versions: 2.3-incubating
> Environment: All
> Reporter: David Wayne Birdsall
> Assignee: David Wayne Birdsall
> Fix For: 2.3-incubating
>
>
> The Optimizer has logic in method ScanOptimizer::useSimpleFileScanOptimizer
> that tries to determine scenarios where a single subset access will clearly
> be optimal, and in those scenarios does not consider MDAM. An example would
> be a query whose only key predicates are equality predicates on a leading
> subset of the key columns.
> However, the logic in ScanOptimizer::useSimpleFileScanOptimizer sometimes
> rules out considering MDAM when it would be beneficial to do so. An example
> is a query with equality predicates on the first two columns of the key, no
> predicates on the third, and equality on the fourth. When the UEC of the
> third column is small, MDAM is likely to be the more efficient plan and
> should be considered.
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