sapdb eat all the memory of my computer

Hello my friend:
I need your help.
When I begin a complete backup, so many processes of sapdb eat all the memory 
of my computer.

cpu: p4 2.0
memory: 1G
data volumes: 20, each of them is 1G
log volumes: 2, each of them is 240M
cache size 6000
log segment size 3000

Please help me. Thanks.