buffer cache

今天看到一ocp关于buffer cache 的题目，在这里记录一下

Which is the correct description of a pinned buffer in the database buffer cache?

A.The buffer is currently being accessed.
B.The buffer is empty and has not been used.
C.The contents of the buffer have changed and must be flushed to the disk by the DBWn process.
D.The buffer is a candidate for immediate aging out and its contents are synchronized with the

block contents on the disk.

Correct Answers:A

解释：

bufer cache 分为free buffer
pinned  buffer  和 dirty buffer 
free 是可以使用的buffer
pinned  buffer 是正在使用的buffer
dirty buffer 是已经改变了的buffer