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Type:
Bug
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Resolution: Duplicate
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Priority:
Minor - P4
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None
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Affects Version/s: 2.0.1
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Component/s: Querying
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Labels:None
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ALL
When only retrieving fields from a covered index, if the fields to be returned are specified with true instead of 1, explain() indicates that the covered index isn't used.
PRIMARY> db.version();
2.0.1
PRIMARY> db.temp.getIndexes();
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"ns" : "test.temp",
"name" : "_id_"
}
]
PRIMARY> db.temp.find({_id:'1'},{_id:true}).explain();
{
"cursor" : "BtreeCursor _id_",
"nscanned" : 0,
"nscannedObjects" : 0,
"n" : 0,
"millis" : 13,
"nYields" : 0,
"nChunkSkips" : 0,
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
"_id" : [
[
"1",
"1"
]
]
}
}
PRIMARY> db.temp.find({_id:'1'},{_id:1}).explain();
{
"cursor" : "BtreeCursor _id_",
"nscanned" : 0,
"nscannedObjects" : 0,
"n" : 0,
"millis" : 0,
"nYields" : 0,
"nChunkSkips" : 0,
"isMultiKey" : false,
"indexOnly" : true,
"indexBounds" : {
"_id" : [
[
"1",
"1"
]
]
}
}
If explain is truly correct here, this seems to violate the principle of least astonishment.
- duplicates
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- Closed
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