While buffers do reside in the buffer cache and buffers are indeed changed, list management acts on buffer headers, not the actual buffers. A buffer header is an optimized in-memory metastructure that contains information about a buffer and its associated block, but does not contain block data such as rows.

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.