Garbage collection v Javě, JVM generace a typy GC aneb způsob automatické správy paměti. Funguje tak, že speciální algoritmus (garbage collector) vyhledává a uvolňuje úseky paměti, které již program nebo proces nepoužívá. Šetří tak váš čas při vývoji.

1. Garbage
Collection in
Java
Ondřej Kratochvíl

2. ▷ Young
Allocation of new objects
Often collected
Minor garbage collection when full - Stop the World event
▷ Old
Stores long surviving objects (also Stop the World)
Major garbage collection
JVM Generations

3. ▷ Permanent (Tenured)
Metadata for JVM
class/method descriptors
Data stored at runtime based on classes in use
Can be collected - when space is needed and JVM does no
longer need some old classes
included in Full garbage collection
JVM Generations

4. ▷ New object is allocated in New generation in eden space
▷ When eden space fills up, minor GC is triggered
Referenced objects are moved to first survivor space, age++
▷ At the next minor GC, referenced objects are moved to
SECOND survivor space
▷ After each minor GC, the spaces switch
▷ If referenced object’s age > threshold, it gets promoted to
Old generation
GC Process - Young generation

5. ▷ Serial GC
Mark-Sweep-Compact algorithm in the old generation
For small memory/small amount of CPU cores
▷ Parallel GC (Throughput GC)
Multithreaded for young generation
▷ Parallel Old GC
Parallel for both generations
▷ CMS GC (Concurrent mark-sweep)
Low pause time
Objects are swept while other are still being marked
GC types

6. Díky za pozornost!
Otázky?
Ondřej Kratochvíl
ondrej.kratochvil@keyup.eu