mongo线程池问题

初始化mongoclient有个maxPoolSize的配置 ，是不是说明此时的mongoclient对象有100个并发数。

如果用db = mongoclient[‘test’]拿到这个db链接是单利还是并发的呢？

如果是单利的，那么用多线程或者多线程，每个都那一个db 能不能优化查询呢？

`maxPoolSize` (optional): The maximum allowable number of
  concurrent connections to each connected server. Requests to a
  server will block if there are `maxPoolSize` outstanding
  connections to the requested server. Defaults to 100. Cannot be 0.
- `minPoolSize` (optional): The minimum required number of concurrent
  connections that the pool will maintain to each connected server.
  Default is 0.