Figure 6-5 shows the relationship between a single buffer header and the various lists. For example, buffer header BH 100 is on LRU 1 and also on CBC 2. Buffer header BH 180 is on CBC 1 and also on Write List 1. A three-dimensional figure would show that a single buffer header always resides on a CBC and either an LRU chain or a write list.

While I will detail the list manipulation in the following sections, manipulation of the three lists occurs at the buffer header level, not at the buffer level, and certainly not at the data block level. Many of us have been taught that while the buffers reside in the buffer cache, the buffers themselves are linked. This is incorrect. Each buffer is associated with a buffer header, and it is the buffer headers that are manipulated in the various lists.

Figure 6-5. Each buffer header resides on a CBC and either an LRU chain or a write list. For example, buffer header BH 150 resides on both LRU 1 and CBC 3.