IBM 000-8697 User Manual

System Architecture

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 to the number of

USERS

divided by 2 and rounded up, up to the value 8.

(Refer to

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

 queue of the queue

pair, and the modified page list is referred to as the

 queue. The two

separate lists eliminate the need to search a queue for a free or unmodified
page.

 illustrates the structure of the

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