Viewing Information on the Old/Young Collection Tab
The name of this tab is dynamically changed when you select a garbage collection instance in the Garbage Collections table. Here you find information about nursery, mark and sweep pause times, etc. (Figure 9-10).
- Nursery Size Before/After-indicates the free space in the nursery before and the free space in the nursery after the garbage collection (in some cases the nursery size increases).
The information below is only valid for old collections:
- Nursery Start/End Position-the starting and ending position in the memory address of nursery.
- Mark/Sweep Phase Time-the time spent in the marking and sweep phases, measured in milliseconds.
- Compacted Size-the size of the heap that has been compacted in the garbage collection.
- Compaction Ratio-the ratio of heap size before and after the compaction, measured in percent.
- Desired/Actual evacuation-the desired evacuation is the size of the area on the Java heap that you want to evacuate and the actual evacuation is the size of the area that JRockit managed to evacuate. The value for actual evacuation can be smaller than the desired due to temporarily pinned objects (objects that are not allowed to be moved during garbage collection). The evacuation takes place during compaction or shrinking of the Java heap.
- GC Reason-indicates the reason for doing this garbage collection.
