IBM 000-8697 OnLine LRU Queues

System Architecture 2-57
OnLine LRU Queues
OnLine LRU Queues
Each regular buffer is tracked through several linked lists of pointers to the
bufferheader table. These linked lists are the least-recently used (LRU) queues.
When OnLine is initialized, the configuration parameterLRUS specifies the
number ofLRU queues or lists to create. The minimum number of LRU
queues is three. The maximum number ofLRU queues is the smaller of two
values: (USERS divided by 2) or 8. The default number of queues created is
equalto the number of USERS divided by 2 and rounded up, up to the value 8.
(Referto page 5-19 for further information about setting the value of LRUS to
improve performance.)
EachLRU queue is actually a pair of linked lists:
■One list tracks free or unmodified pages in the queue.
■One list tracks modified pages in the queue.
The free/unmodified page list is referred to as theFLRU queue of the queue
pair, and the modified page list is referred to as theMLRU queue. The two
separate lists eliminate the need to search a queue for a free or unmodified
page.Figure 2-7 illustrates the structure of the LRU queues.
Figure2-7
The structure of the
LRU queues
LRU queues
Least-recently used------------------------------- Most-recently used
FLRU 1
MLRU 1
Pointerto a modified page in the
buffer header table
Pointer to an empty page in the
buffer header table
Pointerto anunmodified page in
the buffer header table