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https://issues.apache.org/jira/browse/TRAFODION-2259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15547554#comment-15547554
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ASF GitHub Bot commented on TRAFODION-2259:
-------------------------------------------
Github user sandhyasun commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/743#discussion_r81898123
--- Diff: core/sql/generator/GenRelMisc.cpp ---
@@ -3224,6 +3224,9 @@ short Sort::generateTdb(Generator * generator,
sort_tdb->setSortFromTop(sortFromTop());
sort_tdb->setOverflowMode(generator->getOverflowMode());
+
+ sort_tdb->setTopNSize((ULng32)getDefault(GEN_SORT_TOPN_SIZE));
--- End diff --
The size of N should be picked up at runtime in the executor work method.
> Sort TopN operator
> ------------------
>
> Key: TRAFODION-2259
> URL: https://issues.apache.org/jira/browse/TRAFODION-2259
> Project: Apache Trafodion
> Issue Type: Improvement
> Components: sql-exe
> Affects Versions: 2.1-incubating
> Reporter: Prashanth Vasudev
> Assignee: Prashanth Vasudev
>
> Sort operator consumes all records before producing sorted records. For
> certain use cases where only Top N records are required, today sort consumes
> all records into memory and overflows( spills ) to disk. This impacts
> performance.
> if topN is pushed down to sort, only required memory can be allocated and
> sort would only hold topN records in memory. Once all the records are read,
> sorted records in topN is returned.
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