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  1. WiredTiger
  2. WT-7264

Creating a new configuration for search near that allows it to exit quickly when searching for prefixes



    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • None
    • WT10.0.1, 4.4.7, 5.0.0-rc0
    • None
    • 8
    • Storage - Ra 2021-04-05, Storage - Ra 2021-04-19, Storage - Ra 2021-05-03
    • v4.4


      The issue was initially reported as an unusually long load phase in py-tpcc workloads. The issue appears intermittently as a few inserts in the load phase will get stuck for more than a few hours. Related PERF and HELP tickets have more information on the history of the issue.

      bruce.lucas has come up with a standalone reproducer, attached to the ticket.

      When inserting into a unique index, there is potential to get stuck repeatedly searching history store, ie calling __wt_hs_find_upd. We see a very high history store table reads missed statistic in these runs, which convey that these searches through history store are not returning anything. A callgraph that reflects this situation:

      Observed behaviour with the repro script:

      • Observed behaviour in 4.4 is that insert rate is erratic, and a couple of the threads typically seem to get stuck apparently indefinitely with a high rate of missed history store reads with stacks like the above.

      Acceptance criterion:

      • With the repro script: Expected behaviour (same as observed in 4.2) is that insert rate should be steady and each thread should complete at about the same time
      • py-tpcc load phase should not get stuck


        1. 441.png
          114 kB
          Sulabh Mahajan
        2. 442.png
          140 kB
          Sulabh Mahajan
        3. hs.png
          198 kB
          Sulabh Mahajan
        4. image.png
          198 kB
          Dianna Hohensee
        5. image-2021-03-31-17-11-35-375.png
          29 kB
          Luke Pearson
        6. repro.sh
          1 kB
          Sulabh Mahajan

        Issue Links



              luke.pearson@mongodb.com Luke Pearson
              sulabh.mahajan@mongodb.com Sulabh Mahajan
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