Original Description

Add new index option "2dsphereIndexVersion" to 2dsphere indexes.

Version 1 can't index MultiPoint, MultiLineString, MultiPolygon, or GeometryCollection (index build will fail if docs present, and inserting doc will fail if index present). Version 2 can index these.

2.4 builds version 1 indexes, and cannot build/use version 2 indexes. Drop version 2 indexes before downgrading 2.6=>2.4.

2.6 builds version 2 indexes by default, and is able to build/use version 1 too.

Original description:

Documents with 2.6-only GeoJSON types can be missing _id index entries after 2.4 downgrade

The GeoJSON types MultiPoint, MultiLineString, MultiPolygon, and GeometryCollection were introduced in 2.5. As such, version 2.4 of the server cannot unindex these documents from 2dsphere indexes. Attempting to delete such a document after downgrading 2.6=>2.4 will cause the document to be only half-removed: it will be successfully removed from the lower-numbered indexes (like the _id index), but will remain in the 2dsphere and higher-numbered indexes, and will remain in the collection.

Having a collection with missing index entries is problematic, especially for the _id index. Running mongodump against the mongod will generate a dump that is missing these documents (since a snapshot query is issued). If the mongod later becomes a secondary, it will fail to apply updates from the oplog against these documents (since the oplog writers locate such documents with the _id index).

Reproduce with the following, in 2.5.4:

> db.foo.ensureIndex({loc:"2dsphere"})
> db.foo.insert({loc:{type:"MultiPoint",coordinates:[[-73.9580, 40.8003]]}})
Insert WriteResult({ "ok" : 1, "nDocsModified" : 0, "n" : 1 })

Followed by the following, after downgrading to 2.4.8:

> db.foo.validate().keysPerIndex
{ "test.foo.$_id_" : 1, "test.foo.$loc_2dsphere" : 1 }
> db.foo.remove(); db.getLastError()
Can't extract geo keys from object, malformed geometry?:{ type: "MultiPoint", coordinates: [ [ -73.958, 40.8003 ] ] }
> db.foo.validate().keysPerIndex
{ "test.foo.$_id_" : 0, "test.foo.$loc_2dsphere" : 1 }
> db.foo.find().hint({$natural:1}).itcount()
1
> db.foo.find().hint({_id:1}).itcount()
0

At the default logging severity, no log output is generated for this error.