GC Summary Panel
This display shows a collection of statistical information about your garbage
collector trace captured with the -Xverbosegc
or -Xloggc
option.
These measures are
organized into three major sections: Heap Capacity, GC Activity Summary,
and Overall Statistics.
Heap Capacity
This area of the summary display shows capacity information about the Java heap and its components at the beginning and ending of the application, and the peak capacity of each components, along with percentage of the peak utilization of these components.
A rule of thumb for optimal utilization would be to have the Eden space at
100% with the Survivor and Old spaces showing some reserve capacity depending on
the application.
GC Activity Summary
This table presents various summary statistics for each
type of garbage collection event. The value in the last column,
Average rate of collection, can show a dramatic difference in the
performance of different garbage collection event types.
Overall Statistics
This area presents various statistics about the measurement taken:
- Duration of the measurement. This is the total amount of elapsed wall time for
the measurement.
- Total bytes allocated. This is the total amount of space created for new
objects over the lifetime of the application. Do not confuse this with
the amount of memory actually allocated for your program to use!
Instead, it is the amount of memory your program would have consumed had no
garbage collection ever been performed. This is an abstract measure of
the total work done by the application.
-
Residual bytes. This is the heap usage at program
termination.
-
Number of GC events. This is the number of times
the garbage collector was invoked during the program run.
-
Time spent in GC. This is the total amount
of stop_the_world time spent in the garbage collector during the program run.
-
Percentage of time in GC. This is the percentage
of stop_the_world time spent in the garbage collector during the program run.
-
Average allocation rate. This is the average
memory allocation rate for new Java objects.
-
Average ideal allocation rate. This is the average
memory allocation rate for new Java objects with the stop_the_world time
spent in the garbage collector removed. In other words, this is
what the average allocation rate would have been had no garbage collection
been necessary. It is a theoretical limit of your program's
performance if GC time were driven to zero.
-
Incompl_CMS wasted time. This is only available
when -XX:+UseConcMarkSweepGC or -Xconcgc is used with
HP JVM version 1.4.1.05, or 1.4.2 or later. It indicates the stop_the_world time
spent in the incomplete CMS GCs. Since the incomplete CMS did not complete
its GC task, this part of time was wasted.
-
CMS concurrent running time. This is only
available when -XX:+UseConcMarkSweepGC or -Xconcgc is used
with HP JVM version 1.4.1.05, or 1.4.2 or later. It represents the percentage of time
that the concurrent mark-sweep garbage collector was running concurrently
with the application.