-
Type:
Improvement
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Resolution: Won't Fix
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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
Currently count operations that use the $ne operator appear to be ineligible to take advantage of the COUNT_SCAN stage. Such operations currently have the COUNT, FETCH, and IXSCAN stages although no filters are applied in the FETCH stage. The server should be able to generate a COUNT_SCAN plan if there are no benefits to the current implementation.
> db.version()
3.5.7
>
> db.col.explain().count({x:{$ne:1}})
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "test.col",
"indexFilterSet" : false,
"parsedQuery" : {
"$nor" : [
{
"x" : {
"$eq" : 1
}
}
]
},
"winningPlan" : {
"stage" : "COUNT",
"inputStage" : {
"stage" : "FETCH",
"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, 1.0)",
"(1.0, MaxKey]"
]
}
}
}
},
"rejectedPlans" : [ ]
},
"serverInfo" : {
"host" : "",
"port" : 27037,
"version" : "3.5.7",
"gitVersion" : "79c2c2d340982da8b669cd7c3aa6b958dbf56263"
},
"ok" : 1
}
>
> db.col.createIndex({x:1})
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
>
> db.col.explain().count({x:1})
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "test.col",
"indexFilterSet" : false,
"parsedQuery" : {
"x" : {
"$eq" : 1
}
},
"winningPlan" : {
"stage" : "COUNT",
"inputStage" : {
"stage" : "COUNT_SCAN",
"keyPattern" : {
"x" : 1
},
"indexName" : "x_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"x" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"indexBounds" : {
"startKey" : {
"x" : 1
},
"startKeyInclusive" : true,
"endKey" : {
"x" : 1
},
"endKeyInclusive" : true
}
}
},
"rejectedPlans" : [ ]
},
"serverInfo" : {
"host" : "",
"port" : 27037,
"version" : "3.5.7",
"gitVersion" : "79c2c2d340982da8b669cd7c3aa6b958dbf56263"
},
"ok" : 1
}
- is related to
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SERVER-27822 Count plans sometimes don't need a FETCH
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- Closed
-