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From "Jesus Camacho Rodriguez (JIRA)" <>
Subject [jira] [Created] (HIVE-14866) Set hive.limit.optimize.enable to true
Date Fri, 30 Sep 2016 09:01:20 GMT
Jesus Camacho Rodriguez created HIVE-14866:

             Summary: Set hive.limit.optimize.enable to true
                 Key: HIVE-14866
             Project: Hive
          Issue Type: Improvement
    Affects Versions: 2.1.0
            Reporter: Jesus Camacho Rodriguez
            Assignee: Jesus Camacho Rodriguez

Currently, we set up the global limit for the query in two different places through two different
variables: SemanticAnalyzer and through an optimization rule GlobalLimitOptimizer (the latest
is off by default).

This leads to several problems that I have observed:
- Global limit might not be set for very simple queries, e.g., if the query does not contain
a RS). GlobalLimitOptimizer would set the limit in this case, but as stated above, it is off
by default.
- Some other optimizations are not checking both variables, thus missing opportunities.
- The variable set by SemanticAnalyzer does not take into account offset of the query, which
I think might lead to incorrect results if FetchOptimizer kicks in (not verified yet). GlobalLimitOptimizer
does take into account offset of query.

This issue is to set hive.limit.optimize.enable to _true_ by default, i.e., use GlobalLimitOptimizer,
and thus getting rid of the variable set by SemanticAnalyzer. Maybe there are some gaps (cases
covered by SemanticAnalyzer alternative and not covered by GlobalLimitOptimizer) that we will
need to work on.

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