> db.index.find(

{ subdomain: "sub.domain.com"}

,

{ __id:1}

).explain();
{
"cursor" : "BtreeCursor subdomain_1_folder_1_name_1",
"nscanned" : 2002,
"nscannedObjects" : 2002,
"n" : 2002,
"millis" : 6,
"nYields" : 0,
"nChunkSkips" : 0,
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
"subdomain" : [
[
"sub.domain.com",
"sub.domain.com"
]
],
"folder" : [
[

{ "$minElement" : 1 }

,

{ "$maxElement" : 1 }

]
],
"name" : [
[

{ "$minElement" : 1 }

,

{ "$maxElement" : 1 }

]
]
}
}

> db.index.find(

{ subdomain: "sub.domain.org", folder: "" }

,

{subdomain:1}

).explain();
{
"cursor" : "BtreeCursor subdomain_1_folder_1_name_1",
"nscanned" : 1583,
"nscannedObjects" : 1583,
"n" : 1583,
"millis" : 9,
"nYields" : 2,
"nChunkSkips" : 0,
"isMultiKey" : false,
"indexOnly" : false,
"indexBounds" : {
"subdomain" : [
[
"sub.domain.org",
"sub.domain.org"
]
],
"folder" : [
[
"",
""
]
],
"name" : [
[

{ "$minElement" : 1 }

,

{ "$maxElement" : 1 }

]
]
}
}

mongo returns __id in both queries anyway, does that mean mongod needs to scan for objectid in objects and uses some other reference in indexes? i'm confused - it shouldn't touch objects at all for queries like this.