MongoDB operation: Flush ()

Flush () is the force output of the buffer data (note not to be confused with Frush () refresh). 

mainly used in Io, that is, to empty the buffer data, generally in the read and write stream (stream), the data is read into the memory, and then write the data to the file, when you read the data does not mean that your data has been written, because there is still a part of the memory will be left in this buffer. At this point, if you call the Close () method to shut down the read-write stream, then this part of the data is lost, so you should flush () before closing the read-write stream. 

MongoDB operation: Flush ()