[jira] [Created] (IMPALA-7475) Explicitly document perf consequences of setting mem_limit

["Tim Armstrong (JIRA)" <ji...@apache.org>]

Tim Armstrong created IMPALA-7475:
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             Summary: Explicitly document perf consequences of setting mem_limit
                 Key: IMPALA-7475
                 URL: https://issues.apache.org/jira/browse/IMPALA-7475
             Project: IMPALA
          Issue Type: Improvement
          Components: Docs
            Reporter: Tim Armstrong
            Assignee: Alex Rodoni


There are a few significant bits of information that the docs don't really explicitly mention. 
* In the mem_limit docs, we don't mention that Impala will employ various strategies to keep the query's memory consumption under the mem_limit that trade off execution speed for reduced memory consumption.
* Spill-to-disk is one such mechanism but we do other things like reducing number of scanner threads and passing through rows from preaggregations.

[~arodoni_cloudera] is there a good place in the docs to add something like this? I could draft something but not sure exactly where it would fit.



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