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  1. Core Server
  2. SERVER-7959

Potentially unexpected scans with compound indexes when some fields are multikey

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Duplicate
    • 2.2.2
    • None
    • Querying
    • None
    • ALL

    Description

      Lets say you are querying for { a:{ $gt:10, $lt:20 } }

      and you have an index on a, b

      If b is multikey, the query optimizer will scan a much wider range of index and it will have to scan the objects to complete query evaluation. This is because the optimizer doesn't know if all the values of a are scalar; if they are not a document like { _id:2, { a:[ 5, 25 ] } } would match the query.

      This makes the advice that an index on a is not needed if you have an index on a, b incorrect and makes performance optimization confusing.

      Attachments

        Issue Links

          duplicates

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-15086 Allow for efficient range queries over non-array fields in multikey indices

          • Major - P3 - Major loss of function.
          • Closed
          is duplicated by

          Bug - A problem which impairs or prevents the functions of the product. SERVER-8454 Multi-key index prevents bounds being used for non-multi-key part

          • Major - P3 - Major loss of function.
          • Closed
          is related to

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-3173 Planner should use path-level multikey info to generate covered plans when possible

          • Major - P3 - Major loss of function.
          • Closed

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-6050 Consider allowing $elemMatch applied to non arrays

          • Major - P3 - Major loss of function.
          • Closed
          related to

          Bug - A problem which impairs or prevents the functions of the product. SERVER-12470 document and audit multikey bounds behavior

          • Major - P3 - Major loss of function.
          • Closed

          Activity

            People

              hari.khalsa@10gen.com hari.khalsa@10gen.com
              max@10gen.com Max Schireson
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              Dates

                Created:
                Updated:
                Resolved: