IBM 000-8697 Instrukcja Użytkownika Pobierz pdf (Strona 151)

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System Architecture 2-57

OnLine LRU Queues

Each regular buffer is tracked through several linked lists of pointers to the

bufferheadertable.These linked listsarethe least-recentlyused (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

equaltothenumberofUSERSdividedby2androundedup,uptothevalue 8.

(Referto page 5-19for furtherinformationabout setting thevalueof 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

Least-recently used------------------------------- Most-recently used

FLRU 1

MLRU 1

Pointerto amodiﬁedpagein the

buffer header table

Pointer to an empty page in the

buffer header table

Pointertoanunmodiﬁedpagein

the buffer header table

1 2 ... 146 147 148 149 150 151 152 153 154 155 156 ... 701 702

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