Figure 6-4 shows the one-to-one relationship between a buffer header, its associated buffer, and its data block. As illustrated in Figure 6-4, the buffer headers contain, in part, where a buffer resides in the buffer cache, where the associated block resides on disk, and when the buffer was last read from disk. If you hear kernel developers talking about a DBA, they are not referring to you! They are referring to a block's disk address, which is called the data block address, or DBA for short.

Figure 6-4. There is a one-to-one relationship between a buffer header (BH 100), its cached buffer (CB 330), and its on-disk data block (DBA 5,320). List manipulation occurs at the buffer header level, buffer changes occur in the cached buffer, and block changes occur at the disk level.

Have you ever wondered why there is no view v$bc for the buffer cache? That's because a buffer and a block's metadata are stored in the buffer header, and it's the metadata we usually need for our performance analysis. So the view is named v$bh, for buffer header.