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  1. Core Server
  2. SERVER-99092

CE: Estimate is zero in cases where the index key is a tranformation of the original value

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    • Type: Icon: Bug Bug
    • Resolution: Duplicate
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: None
    • Component/s: None
    • None
    • Query Optimization
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db.foo.drop();
db.foo.insertMany([{a: 1}]);
db.foo.createIndex({a: 'hashed'});
db.foo.runCommand({analyze: "foo", key: "a"});
db.adminCommand({setParameter: 1, planRankerMode: "histogramCE"});
db.foo.find({a: 1}).explain().queryPlanner.winningPlan;
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      db.foo.drop(); db.foo.insertMany([{a: 1}]); db.foo.createIndex({a: 'hashed' }); db.foo.runCommand({analyze: "foo" , key: "a" }); db.adminCommand({setParameter: 1, planRankerMode: "histogramCE" }); db.foo.find({a: 1}).explain().queryPlanner.winningPlan;

      In the cases where the index bounds are a transformation of the original bounds, the estimate is zero as the transformed bounds can never be found in the histogram. Cases include:

      • hashed indexes 
            indexBounds: { a: [ '[5902408780260971510, 5902408780260971510]' ] }
      • collations:
              indexBounds: { a: [ '[CollationKey(0x3d0105), CollationKey(0x3d0105)]' ] }

      Timour enumerated the following 3 potential solutions:

      • Do not use histogram CE when the index bounds are transformed (e.g. hashed) constants
      • Store the original bounds in the interval
      • Establish equivalence of interval and predicate, and use the constant from the predicate when the bounds are transformed

            Assignee:
            ben.shteinfeld@mongodb.com Ben Shteinfeld
            Reporter:
            philip.stoev@mongodb.com Philip Stoev
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              Created:
              Updated:
              Resolved: