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Type:
Improvement
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Resolution: Unresolved
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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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Labels:None
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Query Optimization
Consider the following:
> db.foo.find({z:1, $or:[{x:{$in:[1]}},{x:{ $nin:[1]}}]}).explain().queryPlanner.winningPlan
{
"stage" : "FETCH",
"filter" : {
"z" : {
"$eq" : 1
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"x" : 1
},
"indexName" : "x_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"x" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"x" : [
"[MinKey, MaxKey]"
]
}
}
}
Here the database is performing a full index scan which is providing no value. Apart from the scan being unbounded, there is no filter being applied in the IXSCAN stage nor is the index supporting a sort order requested from a client. Such a plan does nothing but slow down the query and therefore should not be considered.