GC in Java 8 get obviously slower compare to Java 7

Question

I have a server with 72 GB memory running, it was use Java 7 with parallel GC and heap size in 25G. But after switch into Java 8, a particular task get much slower. The task basically read a file around 15GB in the memory, and update some relevant data in DB. It usually takes around one hour to finished the job, but after Java 8, it becomes 1.5 hours.

I tried:

1. Increase heap size to 50GB => not help
2. Change GC algorithm from parallel to CMS, it becomes even slower (1.8 hour)

So I am not sure where I can start to have a look, the java library to run the task is still compiled in Java 7 but I am not sure if this relevant? After switch to Java 7, the performance just came back.

Answer 1

To compare/find GC issue, it's better to enable GC logging:

• -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -Xloggc:logs/gc.log

and use GCViewer to parse/visualize GC log files. It will be useful if you gather GC log and attach it to question.

In theory (and practice), Java 8 is faster than Java 7. You mentioned that Java writes data to DB. It may be worth to analyze resource consumption of both, may be DB is root cause.