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https://issues.apache.org/jira/browse/KUDU-2381?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16861340#comment-16861340
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Todd Lipcon commented on KUDU-2381:
-----------------------------------
Looking again at a similar workload and still see behavior like this. An easy
fix is likely to have a new bool like 'DeltaPreparer::_may_have_deltas' which
can be set to true in all of the spots where deleted_, reinserted_, and
updates_by_col_ are modified. We can use that to implement MayHaveDeltas easily
and to short-circuit the clearing of updates_by_col_ for the common case of no
deltas.
> Optimize DeltaMemStore for case of no matching deltas
> -----------------------------------------------------
>
> Key: KUDU-2381
> URL: https://issues.apache.org/jira/browse/KUDU-2381
> Project: Kudu
> Issue Type: Improvement
> Components: perf, tablet
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Major
>
> Currently in a scan workload which scans 280 columns I see DeltaMemStore
> iteration taking up a significant amount of CPU in the scan, despite the fact
> that the dataset has no updates. Of 1.6sec in
> MaterializingIterator::NextBlock, we spent 0.61s in DMSIterator::PrepareBatch
> and 0.14s in DMSIterator::MayHaveDeltas. So, about 46% of our time here is on
> wasted work.
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