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The below query generates three candidate query plans, but explain().allPlans only lists the one chosen. getPlansByQuery() correctly lists all three.
Reproduces in master, and in 2.6.2/2.6.3. Does not reproduce on 2.6.1 or earlier. (edit: does not reproduce on the 2.6 branch; I somehow had my 2.6.x binaries on my machine replaced with binaries from 2.7.x).
> db.foo.drop()
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true
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> db.foo.ensureIndex({b: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.ensureIndex({a:1})
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{
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"createdCollectionAutomatically" : false,
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"numIndexesBefore" : 2,
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"numIndexesAfter" : 3,
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"ok" : 1
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}
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> db.foo.insert({a:1,b:2})
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WriteResult({ "nInserted" : 1 })
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> db.foo.insert({a:1,b:2})
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WriteResult({ "nInserted" : 1 })
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> db.foo.insert({a:1,b:2})
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WriteResult({ "nInserted" : 1 })
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> db.foo.find({a:1,b:1}).itcount()
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0
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> db.foo.getPlanCache().getPlansByQuery({a:1,b:1},{},{}).length
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3
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> db.foo.find({a:1,b:1}).explain(true)
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{
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"cursor" : "BtreeCursor b_1",
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"isMultiKey" : false,
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"n" : 0,
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"nscannedObjects" : 0,
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"nscanned" : 0,
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"nscannedObjectsAllPlans" : 0,
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"nscannedAllPlans" : 0,
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"scanAndOrder" : false,
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"indexOnly" : false,
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"nYields" : 0,
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"nChunkSkips" : 0,
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"millis" : 0,
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"indexBounds" : {
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"b" : [
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[
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1,
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1
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]
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]
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},
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"allPlans" : [
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{
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"cursor" : "BtreeCursor b_1",
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"isMultiKey" : false,
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"n" : 0,
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"nscannedObjects" : 0,
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"nscanned" : 0,
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"scanAndOrder" : false,
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"indexOnly" : false,
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"nChunkSkips" : 0,
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"indexBounds" : {
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"b" : [
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[
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1,
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1
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]
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]
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}
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}
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],
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"server" : "Rassi-MacBook-Pro.local:27017",
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"filterSet" : false,
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"stats" : {
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"type" : "KEEP_MUTATIONS",
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"works" : 2,
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"yields" : 0,
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"unyields" : 0,
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"invalidates" : 0,
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"advanced" : 0,
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"needTime" : 0,
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"isEOF" : 1,
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"children" : [
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{
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"type" : "FETCH",
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"works" : 1,
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"yields" : 0,
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"unyields" : 0,
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"invalidates" : 0,
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"advanced" : 0,
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"needTime" : 0,
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"isEOF" : 1,
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"alreadyHasObj" : 0,
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"forcedFetches" : 0,
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"matchTested" : 0,
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"children" : [
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{
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"type" : "IXSCAN",
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"works" : 1,
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"yields" : 0,
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"unyields" : 0,
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"invalidates" : 0,
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"advanced" : 0,
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"needTime" : 0,
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"isEOF" : 1,
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"keyPattern" : "{ b: 1.0 }",
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"isMultiKey" : 0,
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"boundsVerbose" : "field #0['b']: [1.0, 1.0]",
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"yieldMovedCursor" : 0,
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"dupsTested" : 0,
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"dupsDropped" : 0,
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"seenInvalidated" : 0,
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"matchTested" : 0,
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"keysExamined" : 0,
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"children" : [ ]
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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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>
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