System Architecture 2-59
LRU Queues and Buffer Pool ManagementLRU_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.
TheLRU_MAX_DIRTY configuration parameter limits the number of page
buffers that can be appended to theMLRU queues. The default value of
LRU_MAX_DIRTY is 60, meaning that page cleaning begins when 60 percent
ofthe total number of buffers are modified. (In practice, page cleaning begins
underseveral conditions, only one of which is when an MLRU queue reaches
the specific number that represents this 60 percent limitation. Refer to
page 2-73 for further information about initiating page cleaning.) The
followingexample shows how the value of LRU_MAX_DIRTY is applied to the
buffer pool to arrive at the maximum number of page buffers in anMLRU
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 whichMLRU cleaning can end. The
LRU_MIN_DIRTY configuration parameter specifies the acceptable
percentage of modified buffers in anMLRU queue. The default value of
LRU_MIN_DIRTY is 50, meaning that page cleaning is no longer required
when50 percent of the total number of buffers are modified. In practice, page
cleaning can continue beyond this point as directed by thetbinit daemon
process.