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https://issues.apache.org/jira/browse/DRILL-6574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16547689#comment-16547689
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ASF GitHub Bot commented on DRILL-6574:
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arina-ielchiieva commented on issue #1386: DRILL-6574: Add option to push
LIMIT(0) on top of SCAN (late limit 0 optimization)
URL: https://github.com/apache/drill/pull/1386#issuecomment-405893185
@vvysotskyi could you please review?
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> Add option to push LIMIT(0) on top of SCAN (late limit 0 optimization)
> ----------------------------------------------------------------------
>
> Key: DRILL-6574
> URL: https://issues.apache.org/jira/browse/DRILL-6574
> Project: Apache Drill
> Issue Type: Improvement
> Affects Versions: 1.13.0
> Reporter: Bohdan Kazydub
> Assignee: Bohdan Kazydub
> Priority: Major
> Labels: doc-impacting
> Fix For: 1.14.0
>
>
> Currently we have early limit 0 optimization
> (planner.enable_limit0_optimization) which determines query data types before
> actual scan. Since we not always able to determine data type during planning,
> we need to add one more option to enable late limit 0 optimization
> (planner.enable_limit0_on_scan, exit query right after scan. LIMIT(0) on SCAN
> for UNION and complex functions will be disabled i.e. UNION and complex
> functions need data to produce result schema. This would not work for the
> following list of functions: KVGEN, MAPPIFY, FLATTEN, CONVERT_FROMJSON,
> CONVERT_TOJSON, CONVERT_TOSIMPLEJSON, CONVERT_TOEXTENDEDJSON.
> Query plan examples:
> // todo add two plans before and after the changes
> Also both early and late limit 0 optimization will be turned on by default.
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