> db.people.distinct('city',

{state:'NY'}

).length
1371
> Date.timeFunc(function(){db.people.distinct('city',

{state:'NY'}

)})
14369
> db.people.find(

{state:'NY'}

).explain().millis
1338

db.people.find(

{state:'NY'}

).explain()
{
"cursor" : "BtreeCursor state_1_city_1",
"indexBounds" : [
[
{
"state" : "NY",
"city" :

{ "$minElement" : 1 }

},
{
"state" : "NY",
"city" :

{ "$maxElement" : 1 }

}
]
],
"nscanned" : 1980644,
"nscannedObjects" : 1980644,
"n" : 1980644,
"millis" : 1365,
"oldPlan" : {
"cursor" : "BtreeCursor state_1_city_1",
"indexBounds" : [
[
{
"state" : "NY",
"city" :

{ "$minElement" : 1 }

},
{
"state" : "NY",
"city" :

{ "$maxElement" : 1 }

}
]
]
},
"allPlans" : [
{
"cursor" : "BtreeCursor state_1_city_1",
"indexBounds" : [
[
{
"state" : "NY",
"city" :

{ "$minElement" : 1 }

},
{
"state" : "NY",
"city" :

{ "$maxElement" : 1 }

}
]
]
}
]
}