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 <jianq...@cs.wisc.edu>
Date: 2017-08-02T20:47:30Z
Fix the bug with min/max aggregation.
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