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  1. WiredTiger
  2. WT-76

Improve read performance for variable-length column stores

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    Details

    • Type: Task
    • Status: Closed
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: WT1.0
    • Component/s: None
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      Description

      When profiling skiplists, I discovered that reading from variable-length column stores is over 100x slower than row stores for the TokyoCabinet workload:

      $ cd bench/tcbench
      $ ./wttest write -bulk file:cabinet.wt_b 1000000 > /dev/null
      $ time ./wttest read file:cabinet.wt_b 1000000 > /dev/null

      real 0m4.922s
      user 0m8.222s
      sys 0m1.465s

      $ ./wttest vlcswrite -bulk file:cabinet.vlwt_b 1000000 > /dev/null
      $ time ./wttest vlcsread file:cabinet.vlwt_b 1000000 > /dev/null

      real 26m51.004s
      user 35m31.747s
      sys 6m25.888s
      Profiling shows that is because we do a full scan of the leaf page on every search:

      One way to fix this would be to use the same trick we use for row leaf pages: instead of maintaining an array of offsets to cells, keep an array of pointers, some on-page and some off page. Keep the record number in expanded cells and expand the binary search points.

      vlcs-read-profile.png (49.8 kB) Michael Cahill, 08/04/2011 12:07 am

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              Assignee:
              michael.cahill Michael Cahill
              Reporter:
              wiredtiger WiredTiger
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