Sharded Map Reduce

shardedmapreduce.js

use digg
//Map reduce functions
map = function() {
emit(this.user.name, {diggs: this.diggs, posts: 1});
}

reduce = function(key, values) {
var diggs = 0;
var posts = 0;
values.forEach(function(doc) {
diggs += doc.diggs;
posts += doc.posts;
});
return {diggs: diggs, posts: posts};
}

//Output in the same database to collection digger_users. 
//Works from MongoD and MongoS
db.stories.mapReduce(map, reduce, {out: 'digg_users'});

//Output in different database and collection. 
//Works from MongoD
//Does not work from MongoS - uncaught exception: map reduce failed:{ "ok" : 0, "errmsg" : "can't use out 'db' with non-sharded db" }
db.stories.mapReduce(map, reduce, {out : {replace : "collectionName", db : "otherDB"}});

//Enable sharding on the input database, specify sharded : true
//
sh.enableSharding('digg')
sh.shardCollection('digg.stories',{'_id':1});

db.stories.mapReduce(map, reduce, {out : {replace : "collectionName", db : "otherDB", sharded : true}});

//This one works
db.stories.mapReduce(map, reduce, {out : {replace : "otherDB.collectionName",  sharded : true}});
sh.enableSharding('otherDB')
sh.shardCollection('otherDB.collectionName',{'_id':1});

db.sourcecollection.mapReduce(map, reduce, {out : {replace : "otherDB.collectionName",  sharded : true}});

db.runCommand(
{ mapreduce : 'stories',
map : map,
reduce : reduce,
out : {replace : "otherDB.collectionName",  sharded : true},
verbose : true
})