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  1. Core Server
  2. SERVER-18674

Very low throughput during portion of checkpoint under WiredTiger

    • Type: Icon: Bug Bug
    • Resolution: Done
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: 3.1.3
    • Component/s: WiredTiger
    • Labels:
    • Fully Compatible
    • ALL

      • 132 GB memory, 32 processors, slowish SSDs, 20 GB WT cache
      • YCSB 10 fields/doc, 20M docs, 50/50 workload (zipfian distribution), 20 threads
      • data set size is ~23 GB but cache usage can grow to ~2x that and storage size can grow to ~3x, believe due to random update workload
      • to avoid SERVER-18314 used either of the following (with same results)
        • ext4 mounted with -o commit=10000000
        • xfs

      3.1.3-pre (f5450e9bc5cf63c3dc4d9cb416713b0f6970e6d4)

      3.1.3 (51ad8eff0d50387f0565d23a15e7ba1db0ea962c)

      3.1.4-pre (36ac7a5d8a6cc4f6280f90ce743ab05a77a541a8)


      • issue for this ticket is period from C-D; B-C appears to be different issue.
      • appears to be a regression in 3.1.3
      • same result with xfs and ext4 -o commit=largenumber
      • superficially similar to SERVER-18314 in that it coincides with an fdatasync but:
        • used settings that were shown to eliminate SERVER-18314 issue
        • writes did not seem to be blocked as in SERVER-18314
        • only affected one of the two periods where fadatasync runs
        • so appears to be WT issue, not platform issue
      • attempted to get stack traces but it appears process is not interruptible during the fdatasync and this issue coincides with that

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        4. wtmonitor.html
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            david.hows David Hows
            bruce.lucas@mongodb.com Bruce Lucas (Inactive)
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