Java EE 8 High Performance

Memory

The GC.class_histogram command allows you to get a heap histogram. We will deal with this in the coming sections. But just to sum up very quickly, the heap is where most of your Java objects will go. Therefore, it is important to see how it is used.

If we execute the GC.class_histogram command in our process, the output will look as follows:

$ jcmd 7577 GC.class_histogram7577: num #instances #bytes class name----------------------------------------------   1: 192795 16202648 [C   2: 10490 4667040 [B   3: 191582 4597968 java.lang.String   4: 38779 3412552 java.lang.reflect.Method   5: 20107 2243296 java.lang.Class   6: 70045 2241440 java.util.HashMap$Node   7: 24429 2078312 [Ljava.util.HashMap$Node; 8: 47188 1887520 java.util.LinkedHashMap$Entry ...