I have a compund index consisting of a simple ascending index and a geospatial index:
{ v: 1, key: { PlayerSortMask: 1, RandomGeoIdentifier: "2dsphere" }, ns: "JellyDev.Players", name: "Sort Mask + Random Geo ID", min: 0, max: 1 }
Now I have the following 2 problems:
1. When I try to use the prefix index (querying only on the 1st index), I get a basic cursor used, and not the index I've created:
Query used:
{ "PlayerSortMask" : 2 }
Explain returned:
{ "cursor" : "BasicCursor", "isMultiKey" : false, "n" : 1, "nscannedObjects" : 1, "nscanned" : 1, "nscannedObjectsAllPlans" : 1, "nscannedAllPlans" : 1, "scanAndOrder" : false, "indexOnly" : false, "nYields" : 0, "nChunkSkips" : 0, "millis" : 0, "indexBounds" : { }, "allPlans" : [{ "cursor" : "BasicCursor", "n" : 1, "nscannedObjects" : 1, "nscanned" : 1, "indexBounds" : { } }], "server" : "widmore:10010" }
2. Not sure if this is a problem or not, but when I query using both fields, using $eq & $near, I get the following explain:
{ "cursor" : "S2NearCursor", "isMultiKey" : true, "n" : 1, "nscannedObjects" : 1, "nscanned" : 6, "nscannedObjectsAllPlans" : 1, "nscannedAllPlans" : 6, "scanAndOrder" : false, "indexOnly" : false, "nYields" : 0, "nChunkSkips" : 0, "millis" : 0, "indexBounds" : { }, "nscanned" : NumberLong(6), "matchTested" : NumberLong(1), "geoMatchTested" : NumberLong(1), "numShells" : NumberLong(3), "keyGeoSkip" : NumberLong(5), "returnSkip" : NumberLong(0), "btreeDups" : NumberLong(0), "inAnnulusTested" : NumberLong(1), "allPlans" : [{ "cursor" : "S2NearCursor", "n" : 1, "nscannedObjects" : 1, "nscanned" : 6, "indexBounds" : { } }], "server" : "widmore:10010" }
And this is the query used to fetch the result:
{ "PlayerSortMask" : 2, "RandomGeoIdentifier" : { "$near" : { "$geometry" : { "type" : "Point", "coordinates" : [0.88434365572610107, 0.90583264916475525] } } } }
Now it says it uses the S2NearCursor, but it's obviously not the index I've created - as it has the name Sort Mask + Random Geo ID.
Any help would be greatly appreciated.
For problem 1 there's a known issue in MongoDB with compound geo indexes. https://jira.mongodb.org/browse/SERVER-9257 The problem is fixed in 2.5.4 which is a beta release.
You can workaround this for now by creating an additional simple index on PlayerSortMask.
For problem 2, S2NearCursor means an index is being used. I think the explain "loses" the name and this is a known issue, but I can't remember the bug number.