First, sharding:

> db.adminCommand( { shardcollection : "test.insert_test", key :

{"b":1,"a":1}

});

{ "collectionsharded" : "test.insert_test", "ok" : 1 }

Then splitting (look at 'a' and 'b' order in shard key and split):

> db.adminCommand( { split : "test.insert_test" , middle :

{ 'a' : 0,'b':1 }

} )

{ "ok" : 1 }

> use config
switched to db config
> db.chunks.find()
{ "_id" : "test.insert_test-b_MinKeya_MinKey", "lastmod" :

{ "t" : 1000, "i" : 1 }

, "ns" : "test.insert_test", "min" : { "b" :

{ $minKey : 1 }

, "a" :

{ $minKey : 1 }

}, "max" :

{ "a" : 0, "b" : 1 }

, "shard" : "shard0000" }
{ "_id" : "test.insert_test-a_0.0b_1.0", "lastmod" :

{ "t" : 1000, "i" : 2 }

, "ns" : "test.insert_test", "min" :

{ "a" : 0, "b" : 1 }

, "max" : { "b" :

{ $maxKey : 1 }

, "a" :

{ $maxKey : 1 }

}, "shard" : "shard0000" }

after that any moveChunk command will fail with "Chunk map pointed to incorrect chunk" message, because BSONObj::woCompare, used for searching for a chunk, can't compare

{'a':1,'b':0}

with

{'b':0, 'a':1}