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The execution stats output for explain of a query plan containing the COUNT_SCAN execution stage is missing index bounds information. The other index access stages correctly report their associated index bounds.
> db.foo.drop()
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true
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> db.foo.ensureIndex({a:1})
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{
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"createdCollectionAutomatically" : true,
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"numIndexesBefore" : 1,
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"numIndexesAfter" : 2,
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"ok" : 1
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}
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> db.foo.explain('executionStats').find({a:1}) // Index bounds correctly reported.
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...
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"stage" : "IXSCAN",
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"nReturned" : 0,
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"executionTimeMillisEstimate" : 0,
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"works" : 1,
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"advanced" : 0,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 0,
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"restoreState" : 0,
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"isEOF" : 1,
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"invalidates" : 0,
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"keyPattern" : {
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"a" : 1
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},
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"indexName" : "a_1",
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"isMultiKey" : false,
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 1,
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"direction" : "forward",
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"indexBounds" : {
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"a" : [
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"[1.0, 1.0]"
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]
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},
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...
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> db.foo.explain('executionStats').distinct('a') // Index bounds correctly reported.
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...
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"stage" : "DISTINCT_SCAN",
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"nReturned" : 0,
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"executionTimeMillisEstimate" : 0,
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"works" : 1,
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"advanced" : 0,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 0,
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"restoreState" : 0,
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"isEOF" : 1,
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"invalidates" : 0,
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"keyPattern" : {
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"a" : 1
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},
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"indexName" : "a_1",
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"isMultiKey" : false,
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 1,
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"direction" : "forward",
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"indexBounds" : {
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"a" : [
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"[MinKey, MaxKey]"
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]
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},
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...
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> db.foo.explain('executionStats').count({a:1}) // Index bounds not reported.
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...
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"inputStage" : {
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"stage" : "COUNT_SCAN",
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"nReturned" : 0,
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"executionTimeMillisEstimate" : 0,
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"works" : 1,
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"advanced" : 0,
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"needTime" : 0,
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"needYield" : 0,
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"saveState" : 0,
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"restoreState" : 0,
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"isEOF" : 1,
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"invalidates" : 0,
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"keysExamined" : 1,
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"keyPattern" : {
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"a" : 1
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},
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"indexName" : "a_1",
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"isMultiKey" : false,
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 1
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}
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...
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