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System Architecture 2-57
OnLine LRU Queues
OnLine LRU Queues
Each regular buffer is tracked through several linked lists of pointers to the
buffer header table. These linked lists are the least-recently used (LRU) queues.
When OnLine is initialized, the configuration parameter LRUS specifies the
number of LRU queues or lists to create. The minimum number of LRU
queues is three. The maximum number of LRU queues is the smaller of two
values: (USERS divided by 2) or 8. The default number of queues created is
equal tothe number of USERS divided by 2 and rounded up, up to the value 8.
(Refer to page 5-19 for further information about setting the value of LRUS to
improve performance.)
Each LRU 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 the FLRU queue of the queue
pair, and the modified page list is referred to as the MLRU 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.
Figure 2-7
The structure of the
LRU queues
LRU queues
Least-recently used------------------------------- Most-recently used
FLRU 1
MLRU 1
Pointer to a modified page in the
buffer header table
Pointer to an empty page in the
buffer header table
Pointer to an unmodified page in
the buffer header table