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From sudheeshkatkam <...@git.apache.org>
Subject [GitHub] drill pull request: DRILL-3623: Use shorter query path for LIMIT 0...
Date Thu, 29 Oct 2015 02:20:14 GMT
Github user sudheeshkatkam commented on the pull request:

    https://github.com/apache/drill/pull/193#issuecomment-152053724
  
    I think I see the source of confusion (sorry); this patch does not address that query
in the JIRA, which is why Jinfeng asked me to change the title in one of his comments. Regarding
that query, DRILL-3921 helps avoids most of the execution time, but we still incur the planning
time. And my initial approach address this issue but as mentioned above, this is blocked by
DRILL-2288 and other things.
    
    The new approach actually addresses any query that has a limit 0 above a blocking operator
that consumes all records. And avoiding parallelization made the query much worse. (Actually,
was fast-schema supposed to still kick in? Did not seem like it from my experiments.)
    
    I tested against a query like `SELECT * FROM (SELECT COUNT(DISTINCT a), COUNT(DISTINCT
b), COUNT(DISTINCT c) FROM very_large_table) T LIMIT 0` and this completed two orders of magnitude
faster.


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