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  1. Core Server
  2. SERVER-24401

Allow fast-distinct scan on indexes with non-simple collation

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    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 3.3.12
    • Component/s: Querying
    • Labels:
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      Description

      In getExecutorDistinct(), we use the function turnIxscanIntoDistinctIxscan() to convert an IXSCAN into a DISTINCT_SCAN in a QuerySolution where possible. It only applies to solutions with a PROJECTION as the root, and an IXSCAN as its child. This will not apply to indexes with non-simple collation, because there the IXSCAN stage is always followed by a FETCH stage. It should be possible to convert the IXSCAN into a DISTINCT_SCAN for an index with a non-simple collation anywhere that it is possible for an index with a simple collation.

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