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Type:
Improvement
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Resolution: Won't Do
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: None
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None
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Query Optimization
remove repeat contain index from the relevant candidate indexes, this can avoid some useless calculations.
for example:
{a:1, b:1} contain {a:1}, so we can remove index {a:1} from the candidates
{a:"hashed", b:1} contain {a:"hashed"}, so we can remove index {a:"hahsed"} from the candidates
{a:1, b:1} is better than {a:1},because both cases are satisfied for db.collection.find({a:xx})
and db.collection.find({a:xx,b:xx})