A
MemoryUsage object represents a snapshot of memory usage.
Instances of the
MemoryUsage class are usually constructed
by methods that are used to obtain memory usage
information about individual memory pool of the Java virtual machine or
the heap or non-heap memory of the Java virtual machine as a whole.
A MemoryUsage object contains four values:
init |
represents the initial amount of memory (in bytes) that
the Java virtual machine requests from the operating system
for memory management during startup. The Java virtual machine
may request additional memory from the operating system and
may also release memory to the system over time.
The value of init may be undefined.
|
used |
represents the amount of memory currently used (in bytes).
|
committed |
represents the amount of memory (in bytes) that is
guaranteed to be available for use by the Java virtual machine.
The amount of committed memory may change over time (increase
or decrease). The Java virtual machine may release memory to
the system and committed could be less than init.
committed will always be greater than
or equal to used.
|
max |
represents the maximum amount of memory (in bytes)
that can be used for memory management. Its value may be undefined.
The maximum amount of memory may change over time if defined.
The amount of used and committed memory will always be less than
or equal to max if max is defined.
A memory allocation may fail if it attempts to increase the
used memory such that used > committed even
if used <= max would still be true (for example,
when the system is low on virtual memory).
|
Below is a picture showing an example of a memory pool:
+----------------------------------------------+
+//////////////// | +
+//////////////// | +
+----------------------------------------------+
|--------|
init
|---------------|
used
|---------------------------|
committed
|----------------------------------------------|
max
MXBean Mapping
MemoryUsage is mapped to a
CompositeData
with attributes as specified in the
from
method.