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https://issues.apache.org/jira/browse/IMPALA-8566?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16845048#comment-16845048
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ASF subversion and git services commented on IMPALA-8566:
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Commit f9bf62eefab7fb807f4e5d6900064b612b455a5e in impala's branch
refs/heads/master from Todd Lipcon
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=f9bf62e ]
IMPALA-8566. Fix computation of num_nulls for incremental stats
The calculation for num_nulls in the incremental stats code path
initialized the counter to -1 instead of 0. This meant that, if there
were no nulls (reasonably common), the num_nulls counter would be set to
-1, indicating unknown, rather than 0.
This simply fixes the initialization and updates the tests.
Change-Id: Ie42103ad21d719cac45abc160c8d5422dd33fb28
Reviewed-on: http://gerrit.cloudera.org:8080/13378
Reviewed-by: Impala Public Jenkins <impala-public-jenk...@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenk...@cloudera.com>
> COMPUTE INCREMENTAL STATS sets num_nulls off-by-one
> ---------------------------------------------------
>
> Key: IMPALA-8566
> URL: https://issues.apache.org/jira/browse/IMPALA-8566
> Project: IMPALA
> Issue Type: Bug
> Components: Backend
> Affects Versions: Impala 3.2.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Major
>
> IMPALA-7659 added the population of NULL counts while computing stats, but
> this functionality isn't working properly for incremental stats. The query is
> produced correctly, but the null count set in the table is one lower than it
> should be. In the case that the table has no nulls, this ends up setting a
> '-1' count, which is interpreted as 'unknown'. In the case that there are
> nulls, we'll just be a little inaccurate.
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