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https://issues.apache.org/jira/browse/HIVE-8667?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14192167#comment-14192167
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Ashutosh Chauhan commented on HIVE-8667:
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It seems difference here stems of what rules Hive follows for PPD vs what are
followed in Calcite. Hive PPD pushes filter through both branches of join to
table scans, whereas Calcite is pushing filter only to outer table.
Later in compilation, NullScanOptimizer found that filter only on side and
converted to null-scan, but didnt filter on other side, so didnt do anything
with it.
Also, Calcite changed left outer join to right outer join and swapped tables on
both sides, along with filter.
> CBO: optimize_nullscan - some TableScans for nullscans appeared after CBO
> -------------------------------------------------------------------------
>
> Key: HIVE-8667
> URL: https://issues.apache.org/jira/browse/HIVE-8667
> Project: Hive
> Issue Type: Sub-task
> Components: CBO
> Reporter: Sergey Shelukhin
> Assignee: Sergey Shelukhin
> Fix For: 0.15.0
>
>
> Looks like some rewriting by CBO prevents nullscans from being optimized.
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