Garbage Collection of Oracle JDK6

A simple introduction for GC, mainly about Oracle JDK6.

1. GarbageCollection Don’t you need to pay attention for memory? Kengo TODA 2012/June/13 12೥6݄12೔Ր༵೔
2. Summary for previous Object size = size of header + Σ (field). Array requires contiguous space to store. Why we have to care? 12೥6݄12೔Ր༵೔
3. Answer: Generational Garbage Collection cannot handle too long contiguous space effectively 12೥6݄12೔Ր༵೔
4. What’s GC? Memory management algorithm The reason why we don’t have to `free` in Java 12೥6݄12೔Ր༵೔
5. Type of GC Mark and sweep garbage collection Copying garbage collection Generational garbage collection Garbage first garbage collection (G1GC) etc. 12೥6݄12೔Ր༵೔
6. Currently we use... Generational garbage collection with copying GC for new generation with mark & sweep GC for old generation 12೥6݄12೔Ր༵೔
7. What is Generation? Divide heap into 4 areas Tenured area is ‘old generation’ and others belongs to ‘new generation’ Survivor 1 Survivor 2 Eden Tenured new old 12೥6݄12೔Ր༵೔
8. What is Generation? All data are stored in Eden area at 1st Data is moved by GC Survivor 1 Survivor 2 Eden Tenured new old 12೥6݄12೔Ր༵೔
9. What is Generation? Object data cannot span border If there is no space to put data in specified area, we have to boot GC to keep space Survivor 1 Survivor 2 Eden Tenured new old NG OK OK 12೥6݄12೔Ր༵೔
10. key point Long contiguous space is danger because Throw OOME if it’s longer than heap area (not whole heap size) Boot GC and slow JVM 12೥6݄12೔Ր༵೔
11. References The Java™ Virtual Machine Specification Sensible Sanitation -- Understanding the IBM Java Garbage Collector 12೥6݄12೔Ր༵೔