Fsync理解

Linux 中直接 I/O 机制的介绍：

https://www.ibm.com/developerworks/cn/linux/l-cn-directio/

文件系统缓存，filesystem cache

https://blog.csdn.net/shb_derek1/article/details/99681871

深入理解Fsync

https://www.cnblogs.com/hustcat/archive/2013/08/26/3283955.html

PostgreSQL why not DirectIO for datafile?

http://digoal.lofter.com/post/6ced3_6d2e8a3