HPjmeter 4.3 User's Guide

Table 13 Common Garbage Collection Types Recognized by HPjmeter (continued)
collection and the old generation collection occur independently and
cannot overlap.
Occurs when a background thread is performing a garbage collection
in the old area, but is interrupted when the JVM determines that a full
GC is needed.
Incomplete Concurrent Mark-Sweep
The G1 collector is a server-style garbage collector, targeted for
multi-processor machines with large memories.
Garbage First (G1)
Evacuation Pause means the evacuation pause doesn’t include initial
mark, it chooses a collection set of regions, and evacuates the regions
by copying all their live objects to other locations in the heap.
G1 Evacuation Pause
Initial mark and evacuation pause means the evacuation pause includes
an initial mark; the collector will do an evacuation pause first, then there
will be a G1 concurrent mark cycle.
G1 Initial Mark and Evacuation Pause
This occurs when a G1 background thread is performing garbage
collection, but is interrupted when the JVM determines that a full GC is
needed.
Incomplete Garbage First
Necessary when the old area is expanded on the most recent scavenge.
Typically, this happens when -Xms and -Xmx are not the same.
Old Expanded Full GC
Full GC necessary because the space reserved for metadata is full.Perm Full
Full GC necessary because intermediate space assigned to collection
using the train algorithm is full.
Train Full
Full GC performed when the garbage collector determines that space for
old objects is insufficient to support a successful scavenge. This
determination is reached without analyzing the heap.
Old Too Full
Full GC performed when the garbage collector determines that space for
old objects is insufficient to support a successful scavenge. This
determination is reached by analyzing the heap.
Old Full
The application calls method System.gc() to force a full garbage
collection.
System.gc
A full GC is performed as a result of a signal sent to the JVM to collect
a heap dump.
Heap Dump Triggered GC
A garbage collection is performed as a result of invoking the
ForceGarbageCollection function of JVMTI.
JVMTI force GC
A full garbage collection of unknown type and cause.Other Full GC
Mark the first pause during a concurrent collection cycle. Called the initial
mark, this identifies the initial set of live objects directly reachable from
the application code.
CMS First STW
Mark the second pause during a concurrent collection cycle. Called the
re-mark, this finalizes marking by revisiting any objects that were modified
during the concurrent marking phase.
CMS Second STW
Mark the first pause during a garbage first collection cycle. Called the
re-mark, this finalizes marking by revisiting any objects that were modified
during the concurrent marking phase.
G1 Remark
Mark the second pause during a garbage first collection cycle. Called
the clean-up. The heap regions are sorted for collection priority according
G1 Cleanup
to a cost algorithm. As a result, the regions that will yield the highest
numbers of reclaimed objects, at the smallest cost in terms of time, will
be collected first.
See also Data Collection with -Xverbosegc (page 94).
104 Analyzing Garbage Collection Data