Question

I have a collection, the data look like this:

{
    "_id" : ObjectId("4e627655677c27cf24000000"),
    "gps" : {
        "lng" : 116.343079,
        "lat" : 40.034283
    },
    "lat" : 1351672296
}

And I build a compound index:

{
    "v" : 1,
    "key" : {
        "gps" : "2d",
        "lat" : 1
    },
    "ns" : "test.user",
    "name" : "gps__lat_1"
}

A pure $near query like below can be very fast ( < 20ms ):

>db.user.find({"gps":{"$near":{"lng":116.343079,"lat":40.034283}}}).explain()
{
    "cursor" : "GeoSearchCursor",
    "nscanned" : 100,
    "nscannedObjects" : 100,
    "n" : 100,
    "millis" : 23,
    "nYields" : 0,
    "nChunkSkips" : 0,
    "isMultiKey" : false,
    "indexOnly" : false,
    "indexBounds" : {

    }
}

But the query with “lat” criteria is very slow ( 900ms+ ):

>db.user.find({"gps":{"$near":{"lng":116.343079,"lat":40.034283}},"lat":{"$gt":1351413167}}).explain()
{
    "cursor" : "GeoSearchCursor",
    "nscanned" : 3,
    "nscannedObjects" : 3,
    "n" : 3,
    "millis" : 665,
    "nYields" : 0,
    "nChunkSkips" : 0,
    "isMultiKey" : false,
    "indexOnly" : false,
    "indexBounds" : {

    }
}    

Can anybody explain this? Great thx!

Answer 1

I updated my Mongodb up to 2.2.0, the problem disappeared.

127.0.0.1/test> db.user.find({gps:{$near:[116,40]},lat:{$gt:1351722342}}).explain()
{
    "cursor" : "BasicCursor",
    "isMultiKey" : false,
    "n" : 0,
    "nscannedObjects" : 0,
    "nscanned" : 0,
    "nscannedObjectsAllPlans" : 0,
    "nscannedAllPlans" : 0,
    "scanAndOrder" : false,
    "indexOnly" : false,
    "nYields" : 0,
    "nChunkSkips" : 0,
    "millis" : 0,
    "indexBounds" : {

    },
    "server" : "zhangshenjiamatoMacBook-Air.local:27017"
}