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https://issues.apache.org/jira/browse/KUDU-2380?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16861361#comment-16861361
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Todd Lipcon commented on KUDU-2380:
-----------------------------------
It seems that 7201b0635a448cd244dc598158b13226f14aa0fb improved this for the
case where an entire rowblock is eliminated (either by deletions or by not
matching a predicate). I tested COUNT(*) vs * on a table using a predicate with
no matches and found that KUDU-2381 was responsible for the main difference
between the two.
> Selective predicates when selecting high number of columns burns CPU in
> SerializeRowBlock
> -----------------------------------------------------------------------------------------
>
> Key: KUDU-2380
> URL: https://issues.apache.org/jira/browse/KUDU-2380
> Project: Kudu
> Issue Type: Improvement
> Components: perf, tserver
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Major
> Attachments: pprof.kudu-tserver.samples.cpu.001.pb.gz
>
>
> Testing a table with 280 columns, I found the following performance
> characteristic:
> - scanning all 280 columns with a selective non-key predicate which matches 0
> rows took 8.28s
> - scanning no columns (count query) with the same predicate which matches 0
> rows took 314ms.
> This suggests that we are burning 96% of our CPU doing useless work for this
> query.
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