使用不在的订单

Question

为什么我无法使此查询有效？

db.mydb.find(
    {"LETTER": {
        "$nin": ["a", "b", "c"]
    }
}, {
    "LETTER": 1,
    "LANGUAGE": 1
}).sort( { "LETTER": 1 } );

给出的错误是：

error: {
    "$err" : "Executor error: Overflow sort stage buffered data usage of 33554457 bytes exceeds internal limit of 33554432 bytes",
    "code" : 17144
}