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  1. Couchbase Server
  2. MB-7564

cbhealthchecker uses inaccurate(?) item_alloc_sizes stat for "Average Document Size"

    Details

    • Sprint:
      PCI Team - Sprint 3, PCI Team - Sprint 4

      Description

      The "Average document size" stat in cbhealthchecker comes from the "item_alloc_sizes" histogram in the cbstats timings report.

      I've been told that item_alloc_sizes is just a rough measure on incoming sets to get an average item size, but does not reflect non-resident items or info since a reset, and is not really accurate enough to be called "Average document size".

      Basing on another stat, like ep_kv_size, is preferred I think.

      Having a histogram of item sizes is great, and if it were available and mostly accurate for the entire data set, that would be wonderful. But that sounds like a different feature request for ep-engine.

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        Activity

        Hide
        maria Maria McDuff (Inactive) added a comment -

        per bug scrub: moving to critical. we need in 2.0.2.

        Show
        maria Maria McDuff (Inactive) added a comment - per bug scrub: moving to critical. we need in 2.0.2.
        Hide
        bcui Bin Cui (Inactive) added a comment -

        Use the folllowing formula:

        avg_doc_size = ep_value_size / (curr_items_tot - ep_num_non_resident)

        Show
        bcui Bin Cui (Inactive) added a comment - Use the folllowing formula: avg_doc_size = ep_value_size / (curr_items_tot - ep_num_non_resident)
        Hide
        maria Maria McDuff (Inactive) added a comment -

        pls verify in 2.0.2. thanks.

        Show
        maria Maria McDuff (Inactive) added a comment - pls verify in 2.0.2. thanks.
        Hide
        shashank Shashank Gupta added a comment -

        Verified.

        Followed:
        1) Default bucket with 4M items
        2) Ran cbhealthchecker
        3) cbhealthchecker reports gives Average Document Size as : 660
        4) Then collected stats (ep_value_size, curr_items_tot and ep_num_non_resident) manually using cbstats.
        5) Used the formula.
        6) Got same result : 660.3

        Show
        shashank Shashank Gupta added a comment - Verified. Followed: 1) Default bucket with 4M items 2) Ran cbhealthchecker 3) cbhealthchecker reports gives Average Document Size as : 660 4) Then collected stats (ep_value_size, curr_items_tot and ep_num_non_resident) manually using cbstats. 5) Used the formula. 6) Got same result : 660.3

          People

          • Assignee:
            shashank Shashank Gupta
            Reporter:
            TimSmith Tim Smith (Inactive)
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            Dates

            • Created:
              Updated:
              Resolved:

              Agile

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