Exploiting frequent field values in java objects for reducing heap memory requirements

The capabilities of applications executing on embedded and mobile devices are strongly influenced by memory size limitations. In fact, memory limitations are one of the main reasons that applications run slowly or even crash in embedded/mobile devices. While improvements in technology enable the integration of more memory into embedded devices, the amount memory that can be included is also limited by cost, power consumption, and form factor considerations. Consequently, addressing memory limitations will continue to be of importance. Focusing on embedded Java environments, this paper shows how object compression can improve memory space utilization. The main idea is to make use of the observation that a small set of values tend to appear in some fields of the heap-allocated objects much more frequently than other values. Our analysis shows the existence of such frequent field values in the SpecJVM98 benchmark suite. We then propose two object compression schemes that eliminate/reduce the space occupied by the frequent field values. Our extensive experimental evaluation using a set of eight Java bench-marks shows that these schemes can reduce the minimum heap size allowing Java applications to execute without out-of-memory exceptions by up to 24% (14% on an average).