
9.3 Reducing Hardware Cost 705
Regardless of whether a hierarchical or flat COMA protocol is used, the initial
data set of the application should not fill the entire main or attraction memory, in
order to ensure that enough space is available in the system for a replaced last
(master) copy to find a new residence. To help find replaceable blocks, the attraction
memories should be quite highly associative as well. Not having enough extra (ini-
tially unallocated) memory available for replication can cause performance problems
for several reasons. First, it makes the COMA nature of the machine less effective in
satisfying cache capacity misse