Details
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Improvement
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Resolution: Won't Fix
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Major - P3
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None
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None
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None
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None
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Query
Description
Currently count operations that use the $ne operator appear to be ineligible to take advantage of the COUNT_SCAN stage. Such operations currently have the COUNT, FETCH, and IXSCAN stages although no filters are applied in the FETCH stage. The server should be able to generate a COUNT_SCAN plan if there are no benefits to the current implementation.
> db.version()
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3.5.7
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>
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> db.col.explain().count({x:{$ne:1}})
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{
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"queryPlanner" : {
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"plannerVersion" : 1,
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"namespace" : "test.col",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"$nor" : [
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{
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"x" : {
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"$eq" : 1
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}
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}
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]
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},
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"winningPlan" : {
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"stage" : "COUNT",
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"inputStage" : {
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"stage" : "FETCH",
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"inputStage" : {
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"stage" : "IXSCAN",
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"keyPattern" : {
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"x" : 1
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},
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"indexName" : "x_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"x" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"direction" : "forward",
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"indexBounds" : {
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"x" : [
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"[MinKey, 1.0)",
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"(1.0, MaxKey]"
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]
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}
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}
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}
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},
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"rejectedPlans" : [ ]
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},
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"serverInfo" : {
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"host" : "",
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"port" : 27037,
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"version" : "3.5.7",
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"gitVersion" : "79c2c2d340982da8b669cd7c3aa6b958dbf56263"
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},
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"ok" : 1
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}
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>
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> db.col.createIndex({x: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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>
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> db.col.explain().count({x:1})
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{
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"queryPlanner" : {
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"plannerVersion" : 1,
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"namespace" : "test.col",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"x" : {
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"$eq" : 1
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}
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},
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"winningPlan" : {
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"stage" : "COUNT",
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"inputStage" : {
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"stage" : "COUNT_SCAN",
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"keyPattern" : {
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"x" : 1
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},
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"indexName" : "x_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"x" : [ ]
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},
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"isUnique" : false,
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"isSparse" : false,
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"isPartial" : false,
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"indexVersion" : 2,
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"indexBounds" : {
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"startKey" : {
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"x" : 1
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},
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"startKeyInclusive" : true,
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"endKey" : {
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"x" : 1
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},
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"endKeyInclusive" : true
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}
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}
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},
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"rejectedPlans" : [ ]
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},
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"serverInfo" : {
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"host" : "",
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"port" : 27037,
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"version" : "3.5.7",
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"gitVersion" : "79c2c2d340982da8b669cd7c3aa6b958dbf56263"
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},
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"ok" : 1
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}
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Attachments
Issue Links
- is related to
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SERVER-27822 Count plans sometimes don't need a FETCH
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- Closed
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