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  1. Kudu
  2. KUDU-2866

CFileSet::Iterator::FinishBatch takes a lot of CPU for selective wide table scans

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    Details

    • Type: Improvement
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 1.11.0
    • Component/s: perf, tablet
    • Labels:
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      Description

      Scanning a wide table with a predicate that doesn't ever match showed ~10% CPU usage in CFileSet::Iterator::FinishBatch. Looking at the assembly it seems that the cost was in iterating over the vector<bool> indicating which columns had been prepared. In the case of a selective predicate, only one of the 200+ columns was prepared, and the iteration was quite slow. Instead of using the bitmap, we can instead just keep a list of the prepared column iterators.

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            • Assignee:
              tlipcon Todd Lipcon
              Reporter:
              tlipcon Todd Lipcon
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              • Created:
                Updated:
                Resolved: