which of the following describe situations where mongodb has a clear advantage over a typical relational database? check all apply
  1. developer need to get an application into production quickily
  2. Queries from applications are ad hoc and unpredictable
  3. The data model changes frequently
  4. Many Long running complex transactions are present
  由于mongodb是schema less的所以其初始开发速度异常的快， schema less意味着开发人员可以够少地做模式方案设计，更快将应用投产。 同时由于mongodb是schema less的，所以其数据模型变更几乎不需要做任何操作（alter table add/modify)。 对于ad hoc &unpredictable 特性的、无法预估的查询，mongodb对于字段搜索，范围查询、正则表达查询都支持。查询可以要求返回文件document的部分字段，同时也用上用户自定义的java script函数。 Ad hoc queries MongoDB supports search by field, range queries, regular expression searches. Queries can return specific fields of documents and also include user-defined JavaScript functions. http://en.wikipedia.org/wiki/MongoDB Many Long running complex transactions are present  ==》 显然 mongodb中并不适合运行大的长的事务