IBM 000-8697 Manual Do Utilizador

System Architecture

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

of the total number of buffers are modified. (In practice, page cleaning begins
under several conditions, only one of which is when an

MLRU

queue reaches

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

 for further information about initiating page cleaning.) The

following example shows how the value of

LRU_MAX_DIRTY

is applied to the

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

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

when 50 percent of the total number of buffers are modified. In practice, page
cleaning can continue beyond this point as directed by the tbinit daemon
process.