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https://issues.apache.org/jira/browse/IMPALA-7475?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tim Armstrong reassigned IMPALA-7475:
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    Assignee: Tim Armstrong  (was: Alex Rodoni)

> 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: Tim Armstrong
>            Priority: Major
>
> 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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