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From jianqiao <...@git.apache.org>
Subject [GitHub] incubator-quickstep pull request #277: Fix a bug with min/max aggregation.
Date Fri, 04 Aug 2017 19:58:29 GMT
GitHub user jianqiao opened a pull request:

    https://github.com/apache/incubator-quickstep/pull/277

    Fix a bug with min/max aggregation.

    This PR fixes the bug with min/max aggregation (that produces incorrect results) when
the aggregated column is stored with **leading-zero-truncation compression**.
    
    The bug happens because the untyped value (i.e. a `const void *` pointer) obtained from
the leading-zero-truncation compressed column's corresponding `ValueAccessor` is [the address
of a temporary buffer](https://github.com/apache/incubator-quickstep/blob/master/storage/CompressedColumnStoreValueAccessor.hpp#L112)
-- i.e. the value pointer becomes invalid when the next `accessor->next()` gets called.
[Keeping the value pointer](https://github.com/apache/incubator-quickstep/blob/master/types/operations/comparisons/LiteralComparators-inl.hpp#L546)
across [multiple iterations of](https://github.com/apache/incubator-quickstep/blob/master/types/operations/comparisons/LiteralComparators-inl.hpp#L568)
accessor->next() causes the problem.
    
    The fix is to copy the value pointer's underlying value to a local variable (so that the
value remains valid across iterations of accessor->next()).
    


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

    $ git pull https://github.com/apache/incubator-quickstep fix-compare-aggregate

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

    https://github.com/apache/incubator-quickstep/pull/277.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 #277
    
----
commit f3b792bf532aad41724b91cf88c97fcfbbdc1ea9
Author: Jianqiao Zhu <jianqiao@cs.wisc.edu>
Date:   2017-08-02T20:47:30Z

    Fix the bug with min/max aggregation.

----


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