IBM User Guide for Java V7 on Windows > Troubleshooting and support > Using diagnostic tools > Garbage Collector diagnostic data > Verbose garbage collection logging

Garbage collection increment

A complete garbage collection increment is shown within <gc-start> and <gc-end> tags in the verbose output.

The <gc-start> and <gc-end> tags represent the start and end of a garbage collection increment. Both of these tags include a mem-info section. This section includes information about the current state of the Java™ heap, and any memory used by a specific garbage collection policy.

The <mem type="nursery"> tag shows the amount of free space and total space that is used in the nursery area before and after a scavenge event. The used space is where nursery objects reside and future allocations occur. This space does not account for reserved space in the nursery that is used for flipping survived objects on the next scavenge. The real total nursery size can be calculated as:

reported-total-nursery-size/tilt-ratio

.

The <mem type="tenure"> tag shows the amount of free space and total space that is used in the tenure area before and after a GC event.

The <mem-info> tag shows the cumulative amount of free and total used space in the heap. Similarly, as with total nursery size, this value does not account for survivor space in the nursery. The real total heap size can be calculated as:

reported-total-heap-size + reported-total-nursery-size/tilt-ratio

The <gc-start> and <gc-end> tags contain a context-id attribute that indicates the id of the corresponding garbage collection cycle.

<gc-start id="5" type="scavenge" contextid="4" timestamp="2010-11-23T00:41:32.515">
  <mem-info id="6" free="3042472" total="3670016" percent="82">
    <mem type="nursery" free="0" total="524288" percent="0" />
    <mem type="tenure" free="3042472" total="3145728" percent="96">
      <mem type="soa" free="2885288" total="2988544" percent="96" />
      <mem type="loa" free="157184" total="157184" percent="100" />
    </mem>
    <remembered-set count="1852" />
  </mem-info>
</gc-start>

<gc-end id="8" type="scavenge" contextid="4" durationms="2.204" timestamp="2010-11-
 23T00:41:32.517">
  <mem-info id="9" free="3115152" total="3670016" percent="84">
     <mem type="nursery" free="72680" total="524288" percent="13" />
     <mem type="tenure" free="3042472" total="3145728" percent="96">
       <mem type="soa" free="2885288" total="2988544" percent="96" />
       <mem type="loa" free="157184" total="157184" percent="100" />
     </mem>
     <pending-finalizers system="1" default="0" reference="0" classloader="0" />
     <remembered-set count="1852" />
  </mem-info>
</gc-end>

In the example, the contextid of 4 tells you that this garbage collection increment is part of the garbage collection cycle that has the tag <cycle-start id="4">.

Parent: Verbose garbage collection logging

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