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Covered indexes work with straight cursor reads, but not in memory sorts. However, explain output incorrectly states that the queries are 'indexOnly'.
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> c.find( {}, {_id:0,b:1} ).hint( {a:1,b:1} ).sort( {b:1} ).explain()
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{
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"cursor" : "BtreeCursor a_1_b_1",
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"nscanned" : 0,
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"nscannedObjects" : 0,
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"n" : 0,
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"scanAndOrder" : true,
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"millis" : 1,
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"nYields" : 0,
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"nChunkSkips" : 0,
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"isMultiKey" : false,
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"indexOnly" : true,
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"indexBounds" : {
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"a" : [
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[
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{
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"$minElement" : 1
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},
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{
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"$maxElement" : 1
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}
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]
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],
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"b" : [
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[
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{
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"$minElement" : 1
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},
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{
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"$maxElement" : 1
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}
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]
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]
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},
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"server" : "Aaron-Staples-MacBook-Pro.local:27017"
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}
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