That information is not quite right. It is more accurate to say that there are 10 lists, because there are 5 types of buffers and there is a MAIN and AUXILIARY list for each type. Also, there is no separate hot list. The hot list is a sublist of the main replacement list. Of course, there are separate lists for each working set (LRU latch set) of buffers.
You can see all these structures in BUFFERS dumps. Here is an extract ...
(WS) size: 10000 wsid: 1 state: 0
(WS_REPL_LIST) main_prev: 32aefbc main_next: 32ae51c aux_prev: 32c94a0 aux_next: 32c94a0 curnum: 10000 auxnum: 0
cold: 32a307c hbmax: 5000 hbufs: 5000
(WS_WRITE_LIST) main_prev: 32c94b4 main_next: 32c94b4 aux_prev: 32c94bc aux_next: 32c94bc curnum: 0 auxnum: 0
(WS_PING_LIST) main_prev: 32c94d0 main_next: 32c94d0 aux_prev: 32c94d8 aux_next: 32c94d8 curnum: 0 auxnum: 0
(WS_XOBJ_LIST) main_prev: 32c94ec main_next: 32c94ec aux_prev: 32c94f4 aux_next: 32c94f4 curnum: 0 auxnum: 0
(WS_XRNG_LIST) main_prev: 32c9508 main_next: 32c9508 aux_prev: 32c9510 aux_next: 32c9510 curnum: 0 auxnum: 0
Other than the replacement lists, the other lists are for different types of
write buffers. From the bottom up they are buffers that have to be written for a
checkpoint range call, a checkpoint object call, a ping, or merely because they
are dirty. In each case the main list holds buffers which have yet to be
written, and the auxiliary list holds buffers for which a write is pending.
The auxiliary replacement list holds unpinned buffers for which a write has been
completed, and any other buffers that are immediately reusable. The main
replacement list is what is commonly called the LRU list. The operation of the
LRU list was explained under the heading The 8i buffer cache in the October issue of
Ixora News. You may also be interested in the section on DBWn's new tricks in the September issue.
These 10 lists are mutually exclusive. Each buffer can only be on one of the lists at a time. For completeness it should also be mentioned that dirty buffers are also on a thread checkpoint queue and a file checkpoint queue. These queues are maintained in first modification (low RBA) order and are used to optimize checkpoint processing.
I just took an Oracle internals class and the Oracle instructor mentioned that there are now 5 lists in the buffer cache for 8i: the auxiliary list, the hot list, and the LRU list. He would not give the name or the purpose of the other 2 lists. Have you run across any information concerning these new lists?