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  1. Core Server
  2. SERVER-99135

heuristicCE: $limit can not be costed with index - MONGO_UNIMPLEMENTED_TASSERT

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    • Type: Icon: Bug Bug
    • Resolution: Duplicate
    • Priority: Icon: Major - P3 Major - P3
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    • Affects Version/s: None
    • Component/s: None
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    • Query Optimization
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      db.foo.drop();
db.foo.insert({a:1});
db.foo.createIndex({a:1});
// db.foo.runCommand({analyze: "foo", key: "a"});db.adminCommand({setParameter: 1, planRankerMode: "multiPlanning"});
db.foo.aggregate([ { $limit: 1 } ]).explain();
db.foo.aggregate([ { "$match" : { a:1 }}, {$sort: {b:-1}}, {$limit: 1}]).explain();
db.adminCommand({setParameter: 1, planRankerMode: "heuristicCE"});
db.foo.aggregate([ { $limit: 1 } ]).explain();
db.foo.aggregate([ { "$match" : { a:1 }}, {$sort: {a:1}}, {$limit: 1}]).explain();
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      db.foo.drop(); db.foo.insert({a:1}); db.foo.createIndex({a:1}); // db.foo.runCommand({analyze: "foo" , key: "a" });db.adminCommand({setParameter: 1, planRankerMode: "multiPlanning" }); db.foo.aggregate([ { $limit: 1 } ]).explain(); db.foo.aggregate([ { "$match" : { a:1 }}, {$sort: {b:-1}}, {$limit: 1}]).explain(); db.adminCommand({setParameter: 1, planRankerMode: "heuristicCE" }); db.foo.aggregate([ { $limit: 1 } ]).explain(); db.foo.aggregate([ { "$match" : { a:1 }}, {$sort: {a:1}}, {$limit: 1}]).explain();

      If the `LIMIT` appears as a stand-alone stage in the plan , rather than folded in some other operator, it apparently can not be estimated:

      Enterprise test> db.foo.aggregate([ { $limit: 1 } ]).explain();
MongoServerError[Location9586709]: Hit a MONGO_UNIMPLEMENTED_TASSERT!
Enterprise test> db.foo.aggregate([ { "$match" : { a:1 }}, {$sort: {a:1}}, {$limit: 1}]).explain();
MongoServerError[Location9586709]: Hit a MONGO_UNIMPLEMENTED_TASSERT!

            Assignee:
            Unassigned Unassigned
            Reporter:
            philip.stoev@mongodb.com Philip Stoev
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              Created:
              Updated:
              Resolved: