Memory Monitoring and Management Platform MBeans
External
- http://docs.oracle.com/javase/8/docs/api/java/lang/management/BufferPoolMXBean.html
- http://docs.oracle.com/javase/8/docs/api/java/lang/management/GarbageCollectorMXBean.html
Internal
Memory MBean
Memory MBean implements the MemoryMXBean interface, and exists as a singleton instance in the JVM. The MBean instance is accessible from the platform MBean server, either programmatically by calling ManagementFactory.getMemoryMXBean() method, or by looking up the "java.lang:type=Memory" JMX ObjectName.
Memory MBean exposes information about the heap and the non-heap memory, by returning snapshots in the form of MemoryUsage instances.
The Memory MBean also exposes the "ObjectPendingFinalizationCount" JMX attribute, which is the approximate number for which finalization is pending.
MemoryUsage Instance
MemoryUsage instances represent memory snapshots, and they are used by the JVM to represent both heap and non-heap memory pools. The memory pool snapshot is characterized by four values:
- init - represents the initial amount in bytes the JVM requests from the O/S during startup, for this pool.
- used - represents the amount of used memory, for this pool, in bytes. The value includes the live memory objects and garbage objects that have not been collected yet.
- committed - represents the amount of memory in bytes that is guaranteed to be available for use by the JVM for this pool. The amount of committed memory may increase or decrease over time, as the JVM may release memory to the system. Over time, committed could be less than init.
- max - represents the maximum amount of memory in bytes that can be used for memory management.
HeapMemoryUsage
Represents the MemoryUsage snapshot for all heap's memory pools. The used and committed size of the returned instance is the sum of the corresponding values for all heap memory pools. This is not the case for init and max.
NonHeapMemoryUsage
Represents the MemoryUsage snapshot for all non-heap memory pools. The used and committed size of the returned instance is the sum of the corresponding values for all non-heap memory pools. This is not the case for init and max.
Garbage Collection Initiation
A Full GC can be initiated by invoking the gc() JMX operation. The gc() call is equivalent to calling:
System.gc()
Memory Pool MBeans
Expose statistics about memory pools.
Eden Space
The Eden Space memory pool MBean implements the MemoryPoolMXBean interface. The MBean instance is accessible from the platform MBean server, either programmatically by calling ManagementFactory.getMemoryPoolMXBeans() method, or by looking up the "java.lang:type=MemoryPool,name=PS Eden Space" JMX ObjectName. For more information about the Eden memory pool see:
Memory Manager MBeans
For more details about memory managers, see: