Understanding the Connectivity of Heap Objects ; CU-CS-923-01

Modern garbage collectors partition the set of heap objects to achieve the best performance. For example, generational garbage collectors partition objects by age and focus their efforts on the youngest objects. Partitioning by age works well for many programs because younger objects usually have short lifetimes and thus garbage collection of young objects is often able to free up many objects. However, generational garbage collectors are typically much less efficient for longer-lived objects, and thus prior work has proposed many enhancements to generational collection. Our work explores whether the connectivity of objects can yield useful partitions or improve existing partitioning schemes. We look at both direct (e.g., object A points to object B) and transitive (e.g., object A is reachable from object B) connectivity. Our results indicate that connectivity correlates strongly with object lifetimes and deathtimes and is therefore likely to be useful for partitioning objects. ∗This work is supported by NSF ITR grant CCR-0085792, an IBM Faculty Partnership Award, and an equipment grant from Intel. Any opinions, findings, and conclusions or recommendations expressed in this material are the authors’ and do not necessarily reflect those of the sponsors.