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Type:
Bug
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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: Query Planning
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None
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Query Optimization
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ALL
For queries like this:
db.example.find({first: "X", second: {$gt: "Y", $lt: "Z"}})
If "second" is sometimes an array we cannot generate the bounds ("Y", "Z") without an $elemMatch clause. However, it seems we recognize we cannot "intersect" the bounds, but we don't generate the two alternatives we would without the predicate on "first". See these examples:
// Only one alternative generated, expected two:
{
"explainVersion" : "1",
"queryPlanner" : {
"namespace" : "test.example",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"a" : {
"$eq" : 1
}
},
{
"b" : {
"$lt" : 5
}
},
{
"b" : {
"$gt" : 4
}
}
]
},
"queryHash" : "D57C76E4",
"planCacheKey" : "C15FE4FC",
"maxIndexedOrSolutionsReached" : false,
"maxIndexedAndSolutionsReached" : false,
"maxScansToExplodeReached" : false,
"winningPlan" : {
"stage" : "FETCH",
"filter" : {
"b" : {
"$gt" : 4
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"a" : 1,
"b" : 1
},
"indexName" : "a_1_b_1",
"isMultiKey" : true,
"multiKeyPaths" : {
"a" : [ ],
"b" : [
"b"
]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"a" : [
"[1.0, 1.0]"
],
"b" : [
"[-inf.0, 5.0)"
// Would expect to see another plan with [4, inf.0].
]
}
}
},
"rejectedPlans" : [ ]
},
"command" : {
"find" : "example",
"filter" : {
"a" : 1,
"b" : {
"$gt" : 4,
"$lt" : 5
}
},
"$db" : "test"
},
"serverInfo" : {
"host" : "franklinia",
"port" : 27017,
"version" : "5.0.0-alpha",
"gitVersion" : "unknown"
},
"serverParameters" : {
"internalQueryFacetBufferSizeBytes" : 104857600,
"internalQueryFacetMaxOutputDocSizeBytes" : 104857600,
"internalLookupStageIntermediateDocumentMaxSizeBytes" : 104857600,
"internalDocumentSourceGroupMaxMemoryBytes" : 104857600,
"internalQueryMaxBlockingSortMemoryUsageBytes" : 104857600,
"internalQueryProhibitBlockingMergeOnMongoS" : 0,
"internalQueryMaxAddToSetBytes" : 104857600,
"internalDocumentSourceSetWindowFieldsMaxMemoryBytes" : 104857600
},
"ok" : 1
}
// Positive example without a compound index:
{
"explainVersion" : "1",
"queryPlanner" : {
"namespace" : "test.example2",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"b" : {
"$lt" : 5
}
},
{
"b" : {
"$gt" : 4
}
}
]
},
"queryHash" : "A7B8F6B8",
"planCacheKey" : "A0A41213",
"maxIndexedOrSolutionsReached" : false,
"maxIndexedAndSolutionsReached" : false,
"maxScansToExplodeReached" : false,
"winningPlan" : {
"stage" : "FETCH",
"filter" : {
"b" : {
"$gt" : 4
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"b" : 1
},
"indexName" : "b_1",
"isMultiKey" : true,
"multiKeyPaths" : {
"b" : [
"b"
]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"b" : [
"[-inf.0, 5.0)"
]
}
}
},
"rejectedPlans" : [
{
"stage" : "FETCH",
"filter" : {
"b" : {
"$lt" : 5
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"b" : 1
},
"indexName" : "b_1",
"isMultiKey" : true,
"multiKeyPaths" : {
"b" : [
"b"
]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"b" : [
"(4.0, inf.0]"
]
}
}
}
]
},
"command" : {
"find" : "example2",
"filter" : {
"b" : {
"$gt" : 4,
"$lt" : 5
}
},
"$db" : "test"
},
"serverInfo" : {
"host" : "franklinia",
"port" : 27017,
"version" : "5.0.0-alpha",
"gitVersion" : "unknown"
},
"serverParameters" : {
"internalQueryFacetBufferSizeBytes" : 104857600,
"internalQueryFacetMaxOutputDocSizeBytes" : 104857600,
"internalLookupStageIntermediateDocumentMaxSizeBytes" : 104857600,
"internalDocumentSourceGroupMaxMemoryBytes" : 104857600,
"internalQueryMaxBlockingSortMemoryUsageBytes" : 104857600,
"internalQueryProhibitBlockingMergeOnMongoS" : 0,
"internalQueryMaxAddToSetBytes" : 104857600,
"internalDocumentSourceSetWindowFieldsMaxMemoryBytes" : 104857600
},
"ok" : 1
}
It looks to me like the problem is somewhere in the PlanEnumerator, although I haven't been able to pin down exactly where it is yet.