Linux system overloaded by oracle and not responding

i would like to ask you about the following issue. We have systems having 4 CPUs (4core, intel xeon) and quite a lot of ram (32G or more). it happens that if application (application server jboss for java and our own application system having connection pool handling as well for GUI) starts a lot of requests (maybe a lot of complicated select statements, or some plsqls) the system gets overloaded and does not respond for some time. We are using failover cluster (lifekeeper) and this situation ends in the failover or other symptoms when some parts of the system dont respond. We use orarun to set kernel parameters, huge