Minor - P4 The following pages refer to sparse indexes:
- http://docs.mongodb.org/manual/tutorial/create-a-sparse-index/
- http://docs.mongodb.org/manual/reference/command/createIndexes/
- http://docs.mongodb.org/manual/reference/method/db.collection.ensureIndex/
I came across old documentation in the PHP driver stating that sparse indexes only worked with single-field indexes. Thinking that was incorrect, I decided to try them with compound indexes and found that they will index any documents with at least one of the included fields:
> db.foo.drop()
true
> db.foo.ensureIndex({x:1,y:1},{sparse:true})
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.foo.insert({x:1})
WriteResult({ "nInserted" : 1 })
> db.foo.insert({y:1})
WriteResult({ "nInserted" : 1 })
> db.foo.insert({x:2,y:2})
WriteResult({ "nInserted" : 1 })
> db.foo.insert({z:1})
WriteResult({ "nInserted" : 1 })
> db.foo.find().hint("x_1_y_1")
{ "_id" : ObjectId("535532a190f51aaf07927fbb"), "y" : 1 }
{ "_id" : ObjectId("5355329f90f51aaf07927fba"), "x" : 1 }
{ "_id" : ObjectId("535532a590f51aaf07927fbc"), "x" : 2, "y" : 2 }
Also, our current documentation says that sparse only works with asc/desc indexes. It appears to work with geospatial indexes as well.
> db.foo.drop()
true
> db.foo.ensureIndex({loc:"2d"},{sparse:true})
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.foo.insert({x:1})
WriteResult({ "nInserted" : 1 })
> db.foo.insert({loc:[0,0]})
WriteResult({ "nInserted" : 1 })
> db.foo.find({loc:{$near:[0,0]}})
{ "_id" : ObjectId("5355322e90f51aaf07927fb9"), "loc" : [ 0, 0 ] }
I didn't test text indexes, but that would be another thing to confirm.