// Use mtools to setup the cluster and populate it with data.
$ mlaunch --sharded 2 --single -v
$ mgenerate '{"foo": {"$string": {"length": 10000}}, "bar": "$number", "baz": 0}' -n 20000
 
// Connect to mongos and shard the collection. Disable the balancer so that the data remains imbalanced,
// as there needs to be enough data on one of the shards to exceed the in-memory sort limit.
$ mongo
MongoDB shell version: 2.8.0-rc2
connecting to: test
mongos> db.version()
2.8.0-rc2
mongos> db.adminCommand({enableSharding: "test"})
{ "ok" : 1 }
mongos> db.adminCommand({shardCollection: "test.mgendata", key: {_id: 1}})
{ "collectionsharded" : "test.mgendata", "ok" : 1 }
mongos> sh.disableBalancing("test.mgendata")
 
// Connect to the shard with most of the data. The query succeeds on the shard until the limit
// becomes 3337 or higher. Then it fails due to hitting a memory limit. This is expected behavior.
$ mongo --port 27018
MongoDB shell version: 2.8.0-rc2
connecting to: 127.0.0.1:27018/test
> db.mgendata.count()
17950
> db.mgendata.find().sort({bar: 1}).limit(2000).itcount()
2000
> db.mgendata.find().sort({bar: 1}).limit(3336).itcount()
3336
> db.mgendata.find().sort({bar: 1}).limit(3337).itcount()
2014-12-10T20:39:17.781-0500 I QUERY    Error: error: {
        "$err" : "Executor error: Overflow sort stage buffered data usage of 33563546 bytes exceeds internal limit of 33554432 bytes",
        "code" : 17144
}
    at Error (<anonymous>)
    at DBQuery.next (src/mongo/shell/query.js:259:15)
    at DBQuery.itcount (src/mongo/shell/query.js:352:14)
    at (shell):1:47 at src/mongo/shell/query.js:259
 
// Connect to mongos and do the same thing. This time we hit the memory limit even
// if the limit is small, which is the bug!
mongos> db.mgendata.find().sort({bar: 1}).limit(500).itcount()
2014-12-10T20:41:55.832-0500 I QUERY    Error: error: {
        "$err" : "getMore executor error: Overflow sort stage buffered data usage of 33563546 bytes exceeds internal limit of 33554432 bytes",
        "code" : 17406
}
    at Error (<anonymous>)
    at DBQuery.next (src/mongo/shell/query.js:259:15)
    at DBQuery.itcount (src/mongo/shell/query.js:352:14)
    at (shell):1:46 at src/mongo/shell/query.js:259

st = new ShardingTest({ shards: 2, chunkSize: 1, other: { separateConfig: true, nopreallocj: 1 }});
var db = st.s.getDB('test');                                                                         
var mongosCol = db.getCollection('skip');                                                                  
db.adminCommand({ enableSharding: 'test' });                                                         
db.adminCommand({ shardCollection: 'test.skip', key: { x: 1 }});                                     
                                                                                                     
var i = 0;                                                                                           
var filler = new Array(1024).toString();                                                             
// create enough data to exceed 32MB limit
while (i < 32*1024 ) {                                                                               
    var bulk = []; 
    for (j = 0; j < 1024; j++) {                                                                     
        bulk.push({x:i+j, y:i+j, z:filler});                                                           
    }                                                                                                
    mongosCol.insert(bulk);                                                                     
    i += j;                                                                                          
}                                                                                                    
jsTest.log(mongosCol.count() + " documents in " + mongosCol);                                              
                                                                                                     

// test that direct connect to shard returns a document just below in-mem sort limit
var shardCol = st.shard0.getDB('test').getCollection('skip');
jsTest.log('test query succeeds directly on shard with skip 30000');
assert.eq(1, shardCol.find().sort({y:1}).skip(30000).limit(1).itcount());

// test that exceeding the in-memory sort limit errors on mongod
jsTest.log('test that there's an error on mongos with skip 32000');
assert.throws( function(){ mongosCol.find().sort({y:1}).skip(32000).limit(1).itcount() });

// test that exceeding the in-memory sort limit errors on mongos
jsTest.log('test that there's an error on mongos with skip 32000');
assert.throws( function(){ mongosCol.find().sort({y:1}).skip(32000).limit(1).itcount() });

// test that below limit should succeed on mongos 
jsTest.log('test query succeeds on mongos with skip 30000');
assert.eq(1, mongosCol.find().sort({y:1}).skip(30000).limit(1).itcount());