Java Reference
In-Depth Information
Table A-5. Flags for the CMS collector
Flag
What it does
When to use it
See also
Determines when CMS should
begin background scanning of
the old generation.
When CMS experiences con-
current mode failures, reduces
this value.
Understanding
the CMS Col-
lector
-XX:CMSInitiatingOccupancyFraction= N
Causes CMS to use only
CMSInitiatingOccupancyFraction
to determine when to start
CMS background scanning.
Whenever CMSInitiatingOccu-
pancyFraction is specified.
Understanding
the CMS Col-
lector
-XX:+UseCMSInitiatingOccupancyOnly
Sets the number of threads to
use for CMS background scan-
ning.
When lots of CPU is available
and CMS is experiencing con-
current mode failures.
Understanding
the CMS Col-
lector
-XX:ConcGCThreads= N
Directs CMS to sweep the per-
mgen.
When using CMS with an ap-
plication server that performs
lots of class unloading.
Understanding
the CMS Col-
lector
-XX:+CMSPermGenSweepingEnabled
Determines when CMS should
scan permgen.
When CMSPermGenSweepingEn-
abled is set and full GCs occur
because CMS didn't clean up
permgen fast enough.
Understanding
the CMS Col-
lector
-
XX:CMSInitiatingPermOccupancyFraction= N
Directs CMS to unload classes
after the permgen is scanned.
Whenever CMSPermGenSweep-
ingEnabled is set.
Understanding
the CMS Col-
lector
-XX:+CMSClassUnloadingEnabled
Runs CMS in incremental
mode.
If CPU is limited and you still
must run CMS.
Incremental
CMS
-XX:+CMSIncrementalMode
Affects how often incremental
CMS background threads run.
When using incremental CMS
and experiencing concurrent
mode failures, increase this
value.
Incremental
CMS
-XX:CMSIncrementalModeSafetyFactor= N
Affects how often incremental
CMS background threads run.
When using incremental CMS
and experiencing concurrent
mode failures, increase this
value, though setting CMSIncre-
mentalModeSafetyFactor is pre-
ferred.
Incremental
CMS
-XX:CMSIncrementalDutyCycleMin= N
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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