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
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
page 2-73 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
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
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.
