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https://issues.apache.org/jira/browse/DRILL-8088?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17467842#comment-17467842
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ASF GitHub Bot commented on DRILL-8088:
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jnturton commented on pull request #2412:
URL: https://github.com/apache/drill/pull/2412#issuecomment-1003928988
> Drill was designed to allow vector operations (hence Value Vectors), but
the code was never written. In part because there are no CPU vector
instructions that work with SQL nullable data. Arrow is supposed to have
figured out solutions (Gandiva, is it?) which, perhaps we could consider (but
probably only for non-nullable data.)
Hi @paul-rogers, I think that what Arrow does for computations over nullable
data is store an external null mask and compute results for every record,
including the null ones where the value vector contains either rubbish or some
sentinel value. In a second pass, a null mask is computed for the result.
This results in wasted arithmetic operations for null values, but in practice
that's better than a branch for every value. Quite possibly even for pretty
sparse vectors.
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> Improve expression evaluation performance
> -----------------------------------------
>
> Key: DRILL-8088
> URL: https://issues.apache.org/jira/browse/DRILL-8088
> Project: Apache Drill
> Issue Type: Improvement
> Components: Execution - Codegen
> Reporter: wtf
> Assignee: wtf
> Priority: Minor
>
> Found unnecessary map copy when doing expression evaluation, it will slow
> down the codegen when the query include many "case when" or avg/stddev(the
> reduced expressions include "case when"). In our case, the query include 314
> avg, it takes 3+ seconds to generate the projector expressions(Intel(R)
> Xeon(R) CPU E5-2682 v4 @ 2.50GHz 32cores).
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