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Having index on
{a:1, b:1}
here are some plans:
Good:
> db.ix.explain().find({a:1,b:2},{_id:0,a:1})
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{
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"queryPlanner" : {
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"plannerVersion" : 1,
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"namespace" : "test.ix",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"$and" : [
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{
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"a" : {
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"$eq" : 1
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}
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},
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{
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"b" : {
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"$eq" : 2
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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" : "PROJECTION",
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"transformBy" : {
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"_id" : 0,
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"a" : 1
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},
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"inputStage" : {
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"stage" : "IXSCAN",
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"keyPattern" : {
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"a" : 1,
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"b" : 1
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},
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"indexName" : "a_1_b_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"a" : [ ],
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"b" : [ ]
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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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"a" : [
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"[1.0, 1.0]"
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],
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"b" : [
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"[2.0, 2.0]"
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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" : "altoros4",
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"port" : 34001,
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"version" : "3.5.1-89-g7b68733",
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"gitVersion" : "7b68733fae7ce8d91f9a5fda67b9972c15a20ef0"
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},
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"ok" : 1
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}
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Good:
> db.ix.explain().find({a:1,b:{$ne:2}},{_id:0,a:1})
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{
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"queryPlanner" : {
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"plannerVersion" : 1,
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"namespace" : "test.ix",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"$and" : [
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{
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"a" : {
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"$eq" : 1
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}
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},
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{
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"$nor" : [
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{
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"b" : {
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"$eq" : 2
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}
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}
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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" : "PROJECTION",
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"transformBy" : {
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"_id" : 0,
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"a" : 1
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},
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"inputStage" : {
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"stage" : "IXSCAN",
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"keyPattern" : {
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"a" : 1,
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"b" : 1
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},
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"indexName" : "a_1_b_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"a" : [ ],
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"b" : [ ]
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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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"a" : [
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"[1.0, 1.0]"
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],
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"b" : [
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"[MinKey, 2.0)",
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"(2.0, MaxKey]"
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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" : "altoros4",
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"port" : 34001,
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"version" : "3.5.1-89-g7b68733",
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"gitVersion" : "7b68733fae7ce8d91f9a5fda67b9972c15a20ef0"
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},
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"ok" : 1
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}
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Bad:
> db.ix.explain().find({a:1,b:{$ne:null}},{_id:0,a:1})
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{
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"queryPlanner" : {
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"plannerVersion" : 1,
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"namespace" : "test.ix",
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"indexFilterSet" : false,
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"parsedQuery" : {
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"$and" : [
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{
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"a" : {
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"$eq" : 1
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}
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},
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{
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"$nor" : [
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{
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"b" : {
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"$eq" : null
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}
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}
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]
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}
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]
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},
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"winningPlan" : {
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"stage" : "PROJECTION",
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"transformBy" : {
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"_id" : 0,
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"a" : 1
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},
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"inputStage" : {
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"stage" : "FETCH",
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"filter" : {
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"$nor" : [
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{
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"b" : {
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"$eq" : null
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}
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}
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]
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},
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"inputStage" : {
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"stage" : "IXSCAN",
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"keyPattern" : {
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"a" : 1,
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"b" : 1
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},
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"indexName" : "a_1_b_1",
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"isMultiKey" : false,
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"multiKeyPaths" : {
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"a" : [ ],
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"b" : [ ]
|
},
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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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"a" : [
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"[1.0, 1.0]"
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],
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"b" : [
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"[MinKey, null)",
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"(null, 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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"serverInfo" : {
|
"host" : "altoros4",
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"port" : 34001,
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"version" : "3.5.1-89-g7b68733",
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"gitVersion" : "7b68733fae7ce8d91f9a5fda67b9972c15a20ef0"
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},
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"ok" : 1
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}
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Why is there a FETCH to compare b!=null? Seems like a bug.
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