IBM 000-8697 Instrukcja Użytkownika Pobierz pdf (Strona 153)

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101

System Architecture 2-59

LRU Queues and Buffer Pool Management

LRU_MAX_DIRTY

Periodically, the modiﬁed buffers in the MLRU queue are written (ﬂushed)to

disk by the page-cleaner daemons. You can specify the point at which

cleaning begins.

The

LRU_MAX_DIRTY conﬁguration parameter limits the number of page

buffers that can be appended to the MLRU queues. The default value of

LRU_MAX_DIRTY is 60, meaning that page cleaning begins when 60 percent

ofthetotalnumberofbuffersaremodiﬁed. (Inpractice,pagecleaningbegins

underseveral conditions, onlyoneof which iswhenanMLRU queuereaches

the speciﬁc number that represents this 60 percent limitation. Refer to

page 2-73 for further information about initiating page cleaning.) The

followingexampleshowshowthevalueofLRU_MAX_DIRTYisappliedtothe

buffer pool to arrive at the maximum number of page buffers in an MLRU

queue:

BUFFERS specified as 8000

LRUS specified as 8

LRU_MAX_DIRTY specified as 60

Cleaning begins when the number of buffers in the MLRU queue is

equal to (Total buffers/LRU queues) multiplied by LRU_MAX_DIRTY

percentage.

Buffers in MLRU = (8000/8)

60%

Buffers in MLRU = 1000

0.60

Buffers in MLRU = 600

LRU_MIN_DIRTY

You can also specify the point at which MLRU cleaning can end. The

LRU_MIN_DIRTY conﬁguration parameter speciﬁes the acceptable

percentage of modiﬁed buffers in an MLRU queue. The default value of

LRU_MIN_DIRTY is 50, meaning that page cleaning is no longer required

when50percentofthetotalnumber ofbuffersaremodiﬁed.Inpractice,page

cleaning can continue beyond this point as directed by the tbinit daemon

process.

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