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Posted to issues@spark.apache.org by "Liang-Chi Hsieh (JIRA)" <ji...@apache.org> on 2018/09/06 04:43:00 UTC

[jira] [Created] (SPARK-25352) Perform ordered global limit when limit number is bigger than topKSortFallbackThreshold

Liang-Chi Hsieh created SPARK-25352:
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             Summary: Perform ordered global limit when limit number is bigger than topKSortFallbackThreshold
                 Key: SPARK-25352
                 URL: https://issues.apache.org/jira/browse/SPARK-25352
             Project: Spark
          Issue Type: Bug
          Components: SQL
    Affects Versions: 2.4.0
            Reporter: Liang-Chi Hsieh


We have optimization on global limit to evenly distribute limit rows across all partitions. This optimization doesn't work for ordered results.

For a query ending with sort + limit, in most cases it is performed by `TakeOrderedAndProjectExec`.

But if limit number is bigger than `SQLConf.TOP_K_SORT_FALLBACK_THRESHOLD`, global limit will be used. At this moment, we need to do ordered global limit.





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