sh.enableSharding( "test" ) sh.shardCollection( "test.sharded" ,{a:1}) for (i=0;i<100;i++){db.sharded.insert({a:i})} for (i=0;i<10;i++){sh.splitFind( "test.sharded" ,{a:i})} // Wait for the balancer to distirbute the chunk // No sort stage db.sharded.explain().find().sort({a:1}) // SORT_KEY_GENERATOR stage db.sharded.explain().aggregate([{$sort:{a:1}}]) // SORT_KEY_GENERATOR is not shown if the aggregation impacts only one shard db.sharded.explain().aggregate([{$match:{a:{$gt:50}}},{$sort:{a:1}}] )