A 5 minutes ignite talk about garbage collection pauses and overhead. The talk was given in Reversim Summit 2015 Israel

1. Reversim
Summit
2015
JVM
Garbage
Collection
logs,
you
do
not
want
to
ignore
them!
Haim Yadid - Performize-IT

2. 3
2
1

4. About
Me:
Haim
Yadid
•22 Years of SW development experience
•Performance Expert
•Consulting R&D
•Training
http://il.linkedin.com/in/haimyadid
lifey@performize-it.com
www.performize-it.com
blog.performize-it.com
https://github.com/lifey
@lifeyx

6. GC
•You allocate
• myObject = new MyClass(2015)
•GC cleans
•So everything is cool !

8. Responsiveness?

9. Overhead
GCtime
—————
Total
Time

10. Logging GC activity
Add the following to the command line
-XX:+PrintGCDetails
-XX:+PrintGCTimeStamps
-XX:+PrintGCDateStamps
-Xloggc:<logfile>

11. When should I use it ?
Always
In production ?

13. Log File Rotation
-XX:+UseGCLogFileRotation
Control log file size
-XX:GCLogFileSize=1000
Number of log files
-XX:NumberOfGCLogFiles=10
Starting from Java 7
Tuning Memory: Tuning GC

14. The GC Log
2014-03-04T14:58:04.184+0000: 112134.528:
[Full GC [PSYoungGen: 1987780K-
>0K(266920448K)] [ParOldGen: 536855033K-
>340775638K(538269056K)] 538842813K-
>340775638K(805189504K) [PSPermGen: 38132K-
>38120K(67968K)], 310.6279200 secs]
[Times: user=5357.69
sys=2.73,
real=310.64 secs]

15. Whats nice about GC log
They are not human readable
Takes time and knowledge to understand
Not machine readable
Good luck writing a parser

16. GCViewer

17. JClarity: Censum
Commercial product

18. What can we do about it ?

19. So what are we doing with it?
Overhead should be
less than 5%
Usually high overhead is due
to heap too small
Make your heap larger and
reduce overhead

20. So what are we doing with it?
shenandoah
reduce
footprint
Tune
JVM