Logeek Night Kyiv (07 Dec)

1. Java Behind The Scenes
Igor Dmitriev #LTS Logeek Night, Kyiv 2016

2. Igor Dmitriev
ihor.dmitriiev@gmail.com
ihor_dmitriiev
ihor_dmitriiev
igor-dmitriev-3a29b15a

7. Empty ArrayList is iniIalized with
Object array of size 10:
Object[] elementData = new Object[10];

10. Delombok

11. Nathan Reynolds
Is an Architect at
and works in PSR(Performance,
Scalability and Reliability),
team dedicated towards
opImizing Oracle Middleware
soVware. He is the Exalogic
Performance Architect.
In this role, he oversees the technical aspects of analyzing
profiles, figuring out opImizaIons, opImizing code and
measuring performance impact.

12. Analysed 670 Java heap dumps from different
Java programs to find out memory hogs.
Most popular objects: String, char[], Object[],
ArrayList, HashMap
Heap usage per collecIon: 20.1%
- Unused collecIons
- Small collecIons, 4 or fewer elements (most
significant problem)
- Sparse collecIons, capacity is 2 Imes or more
than what you need

13. jdk 1.7.0_40 ArrayList

15. jdk 1.7.0_40 HashMap

16. jdk 1.8.0_25 HashMap

17. jdk 1.8.0_b132 HashMap
hash collision

19. - Node<K,V>[] table[10]
- table.length = 64
- O(n)
- Client(number)

21. - Node<K,V>[] table[10]
- table.length = 64
- O(logn)
- Client(number)

23. Non-comparable Client

24. HashMap
When?

25. How?
Comparable
Comparable is used

26. Non-comparable
If key classes are equal – idenItyHashCode,
otherwise - className.compareTo

27. Why do we get a tree when we add 11 element?

28. ConcurrentHashMap
jdk 1.7.0_40
- concurrencyLevel (default 16)
- Segment
- Retrieval operaIons are non-blocking
- Fail-safe iterator
- sun.misc.Unsafe is used for concurrency
operaIons

30. jdk 1.8.0_25
Changes
- No longer has segments - linked array
- Balanced tree instead of linked list for huge
collisions

33. Useful references
Java Memory Hogs hjps://www.youtube.com/watch?v=gz4LFnOstes
Java Language and Plamorm Futures: A Sneak Peek by Brian Goetz
hjps://www.youtube.com/watch?v=oGll155-vuQ
Алексей Шипилёв — О чём молчат Heap Dump-ы
hjps://www.youtube.com/watch?v=r_bnfv-nlcs
Алексей Шипилёв — Катехизис java.lang.String
hjps://www.youtube.com/watch?v=SZFe3m1DV1A
JDK Release Notes
hjp://www.oracle.com/technetwork/java/javase/jdk-relnotes-
index-2162236.html