GC Summary Panel

This display shows a collection of statistical information about your garbage collector trace captured with the -Xverbosegc option.  A description of each item follows:

  1. Duration of the measurement.  This is the approximate elapsed wall time for the entire data collection
  2. Heap Capacity.  This shows the initial and final heap sizes, along with the sizes of the individual heap spaces.
  3. Capacity Utilization.  This shows the highest percentage utilization of the heap at its final capacity configuration.  That is, given the final heap capacity shown in item 2 above, these are the highest percentages of those areas actually used by the application.  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.
  4. 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.
  5. Residual Bytes.  This is the heap usage at program termination.
  6. Number of GC Events.  This is the number of times the garbage collector was invoked during the program run.
  7. Time Spend in GC.  This is the total amount of wall time spent in the garbage collector during the program run.
  8. Percentage of Time in GC.  This is the percentage wall time spent in the garbage collector during the program run.
  9. Average Allocation Rate.   This is the average memory allocation rate for new Java objects.
  10. Average Ideal Allocation Rate.  This is the average memory allocation rate for new Java objects with the 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.
  11. GC Activity Summary.  This table collects information broken out by garbage collection type.  The information in each column is as follows:
    Last Occur (s) Time at which this GC event last occurred.
    Count Total number of times this GC event occurred.
    Interval (s) Average amount of time between events of this type.
    Duration (s) Average amount of time spent in events of this type.
    Average collection rate (KB/s) Average rate of space recovered by events of this type.