ABSTRACT
The goal of a collector is to find dead objects and reclaim the space they occupy. Tracing collectors (and copying collectors in particular) are most efficient if the space they manage contains few live objects. On the other hand, long-lived objects are handled poorly if the collector processes them repeatedly, either marking and sweeping or copying them again and again from one semispace to another. We noted in Chapter 3 that long-lived objects tend to accumulate in the bottom of a heap managed by a mark-compact collector, and that some collectors avoid compacting this dense prefix. While this eliminates the cost of relocating these objects, they must still be traced and all references they contain must be updated.
