If a single graph has greater memory demands than maximum heap memory limit for the Server, then such graph cannot be successfuly run on said Server. In this situation you can increase the maximal heap memory size, but leave some of your RAM unallocated, and/or optimize your graph, so its memory demands would decrease. I cannot advise you any specific value of the maximum heap memory as it depends on complexity of the graph and size of the processed data. If you want me to help you with the optimization, please send me the graph and a sample of your input data. If the graph and the data correspond with your previous topic, it is ok to send them just once.