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https://issues.apache.org/jira/browse/KUDU-2847?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16861508#comment-16861508
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Todd Lipcon commented on KUDU-2847:
-----------------------------------
Couple ideas:
- convert the bitmap to a list of set indexes once per block, and then iterate
over the list of indexes once per column
- implement the above with some smarter code vs iterating over and testing each
bit (eg
https://lemire.me/blog/2018/03/08/iterating-over-set-bits-quickly-simd-edition/)
-- maybe worth special casing some code for runs of 'all-set' and 'all-unset'
since a lot of SQL predicates tend to be either very dense or very sparse
- codegen for SerializeRowBlock to operate by row instead of by column would
probably yield large benefits as well
> Optimize iteration over selection vector in SerializeRowBlock
> -------------------------------------------------------------
>
> Key: KUDU-2847
> URL: https://issues.apache.org/jira/browse/KUDU-2847
> Project: Kudu
> Issue Type: Improvement
> Components: perf, tserver
> Reporter: Todd Lipcon
> Priority: Major
>
> Currently, SerializeRowBlock operates column-by-column, which means we have
> to iterate over the selection bitmap once for each column. This code isn't
> particularly well optimized -- in TPCH Q6, about 10% of CPU is spent in
> BitmapFindFirst. We should look at alternate implementations here that better
> amortize the bitmap iteration cost across all of the columns and generally
> micro-optimize it.
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