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In following question: Possible Spring Boot or Spring Security Memory Leak
The user prints the java objects as follows:
num #instances #bytes class name
----------------------------------------------
1: 395984 32564344 [C
2: 388697 9328728 java.lang.String
3: 61258 5915088 [B
4: 100297 4814256 java.util.HashMap
5: 50892 4478496 org.apache.catalina.session.StandardSession
6: 58774 3656824 [Ljava.util.HashMap$Node;
7: 84773 3390920 java.util.TreeMap$Entry
8: 51522 3339304 [Ljava.util.Hashtable$Entry;
9: 51834 3317376 java.util.concurrent.ConcurrentHashMap
10: 102111 3267552 java.util.HashMap$Node
11: 96256 3080192 java.util.concurrent.ConcurrentHashMap$Node
12: 24101 2754560 [Ljava.util.concurrent.ConcurrentHashMap$Node;
13: 51472 2470656 java.util.Hashtable
14: 55102 2204080 java.util.LinkedHashMap$Entry
15: 83020 1992480 java.util.ArrayList
16: 34353 1923768 java.util.LinkedHashMap
17: 59156 1892992 org.springframework.boot.loader.util.AsciiBytes
18: 29574 1656144 org.springframework.boot.loader.jar.JarEntryData
19: 18029 1586552 java.lang.reflect.Method
20: 28391 1562080 [Ljava.lang.Object;
21: 37178 1487120 java.lang.ref.SoftReference
22: 47648 1446600 [I
23: 52337 1256088 java.lang.Long
24: 26134 1254432 java.util.TreeMap
25: 50904 1221696 java.beans.PropertyChangeSupport
26: 11777 1214464 java.lang.Class
27: 23748 1139904 org.springframework.security.oauth2.provider.OAuth2Request
28: 35994 863856 java.util.Collections$UnmodifiableRandomAccessList
29: 50904 814464 java.beans.PropertyChangeSupport$PropertyChangeListenerMap
30: 50892 814272 org.apache.catalina.session.StandardSessionFacade
31: 49748 795968 java.util.HashSet
32: 24066 770112 java.util.Collections$UnmodifiableMap
33: 23748 759936 org.springframework.security.oauth2.provider.OAuth2Authentication
34: 23748 759936 org.springframework.security.oauth2.provider.authentication.OAuth2AuthenticationDetails
35: 26000 624000 javax.management.openmbean.CompositeDataSupport
36: 12015 576664 [Ljava.lang.String;
37: 16319 522208 com.sun.org.apache.xerces.internal.xni.QName
38: 15288 489216 java.lang.ref.WeakReference
39: 26448 423168 java.util.LinkedHashSet
40: 26011 416176 java.util.TreeMap$KeySet
What command did the user use to print this info?
Btw, I have added following arguments to my java process.
-XX:+PrintGCDetails -XX:+PrintGCTimeStamps -Xloggc:gc.log -verbose:gc
I hope I have phrased the question correctly.
448
Object references consume 4 bytes. boolean and byte values consume 1 byte. short and char values consume 2 bytes. int and float values consume 4 bytes.
In Java, you can access memory statistics via the Runtime class as follows: Runtime rt = Runtime. getRuntime();
In Java, all objects are dynamically allocated on Heap. This is different from C++ where objects can be allocated memory either on Stack or on Heap. In C++, when we allocate the object using new(), the object is allocated on Heap, otherwise on Stack if not global or static.
getsizeof() function can be done to find the storage size of a particular object that occupies some space in the memory. This function returns the size of the object in bytes. It takes at most two arguments i.e Object itself.
That is the output from jmap -histo. Possibly jmap -histo:live. You run it as an external tool and supply the pid of the JVM. It is provided in the bin directory of your jdk installation.
It is typically safe to run in production but you should be aware of that jmap -histo:live triggers a full GC, which is necessary to only show the live objects. jmap -histo does not trigger a GC.
jmap documentation
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Alternatively you can create a heap-dump. And then use the jmap utility to obtain a histogram from the heap dump. If you are using IBM's JDK you can use IBM's Memory Analyzer tool (MAT) to get the histogram
https://docs.oracle.com/javase/7/docs/webnotes/tsg/TSG-VM/html/memleaks.html#gbywm http://www.ibm.com/developerworks/java/jdk/tools/memoryanalyzer/
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