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    Type:New Feature 
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    Resolution: Done
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    Priority:Major - P3 
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    Affects Version/s: None
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    Component/s: Querying
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Things to keep in mind:
count/distinct
performance check
- is depended on by
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                    SERVER-9547 min() / max() with descending order sort not working -         
- Closed
 
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- is duplicated by
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                    SERVER-5014 $returnKey operator not implemented for getmore -         
- Closed
 
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                    SERVER-7509 Combine index ranges for dotted fields within a $elemMatch expression, when possible -         
- Closed
 
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                    SERVER-12055 Use better bounds (like undefined) when matching empty array -         
- Closed
 
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                    SERVER-6868 prevent use of positional projection with a simple _id query; assert if a positional projection is requested and no match details are supplied -         
- Closed
 
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                    SERVER-4187 automatically pick sparse indexes for $exists:true queries -         
- Closed
 
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                    SERVER-6506 avoid checking for match of a full document field in certain cases where the field was already matched in the index -         
- Closed
 
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                    SERVER-8790 Introduce composable "stages" in query execution -         
- Closed
 
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- is related to
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                    SERVER-8688 Explain output should include index spec -         
- Closed
 
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                    SERVER-12124 "text" command on nonexistent collection trips fatal assertion in mongod -         
- Closed
 
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                    SERVER-12277 Don't generate plans for $text queries which force a non-text index -         
- Closed
 
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                    SERVER-13271 remove surplus projection from distinct -         
- Closed
 
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                    SERVER-12089 Error message unclear for $text query on collection with no text index -         
- Closed
 
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- related to
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                    SERVER-7945 use plan ordering when reporting "winning" plan at the top of explain -         
- Closed
 
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                    SERVER-1116 qo recover from stale index -         
- Closed
 
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                    SERVER-4062 Quoted strings in $near query results in [0,0] coordinates -         
- Closed
 
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                    SERVER-4953 clean/fix exception handling in query plan runners -         
- Closed
 
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                    SERVER-3758 push limit down into index scan for sort + limit queries -         
- Backlog
 
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                    SERVER-12024 re-implement $in in terms of $or -         
- Backlog
 
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                    SERVER-4485 unify index suitability code -         
- Closed
 
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                    SERVER-4671 prefer indexes with equality match on a unique key -         
- Closed
 
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                    SERVER-11987 optimize sort stage with limit -         
- Closed
 
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