The objects (such as Projects, Activities, Assignments, etc.) are stored in the Java Virtual Machine (JVM) heap allocation. Most of these objects are short-lived and are periodically cleaned up by the JVM's garbage collection mechanism.
An increase of concurrent users causes the number of objects in the heap to increase. The resulting congestion and higher frequency of garbage collection can impact the performance and scalability of the system.
Increasing the JVM heap (with the adequate physical memory provisioned) is an efficient way to achieve the desired performance and scalability. See Deployment Categories for guidelines on configuring the optimal JVM heap size.