Command Line Options for Java Garbage Collection Tuning

In my last blog entry I gave a simple overview of how GC or garbage collection works in Java. In this post i list some of the command line options which i found very useful for GC tuning and performance measurement.

Command	Details
-verbose:gc	Prints information at every collection
-XX:+PrintGCDetails	Prints detailed info of GC
-XX:+PrintGCTimeStamps	Will additionally print a time stamp at the start of each collection
-XX:MinHeapFreeRatio=<minimum>	If the percent of free space in a generation falls below <minimum>% the size of the generation will be expanded so as to have <minimum>% of the space free assuming the size of the generation has not already reached its limit.
-XX:MaxHeapFreeRatio=<maximum>	If the percent of free space exceeds <maximum>% the size of the generation will be shrunk so as to have only <maximum>% of the space free as long as shrinking the generation does not decrease it below the minimum size of the generation.
-XX:NewRatio=ratioValue	The young generation size is controlled by NewRatio. For example setting -XX:NewRatio=3 means that the ratio between the young and tenured generation is 1:3.
-XX:NewSize	Determines the lower limit of young gen size
-XX:MaxNewSize	Determines the uppper limit of young gen size
-XX:SurvivorRatio=ratioValue	Sets the ratio between each survivor space and eden to be 1:ratioValue. Each survivor space will be 1/(ratioValue+2) of the young generation (as there are two survivor spaces).
-XX:+PrintTenuringDistribution	Can be used to show this threshold and the ages of objects in the new generation.
-XX:ParallelGCThreads=<desired number>	Determines the number of threads dedicated to Parallel GC.
-XX:MaxGCPauseMillis=<nnn>	Determines the maximum pause time for GC
-XX:GCTimeRatio=<nnn>	Sets the ratio of garbage collection time to application time to 1 / (1 + <nnn>) For example -XX:GCTimeRatio=19 sets a goal of 5% of the total time for garbage collection. By default the goal for total time for garbage collection is 1%.
-XX:YoungGenerationSizeIncrement=<nnn >	Grows the size of young generation by nnn percent.
-XX:TenuredGenerationSizeIncrement=<nnn>	Grows the size of tenured generation by nnn percent.
-XX:MaxPermSize=<desired size>	Sets uppper limit of permanent gen size
-XX:+ TraceClassloading	Know what classes are being loaded
-XX:+ TraceClassUnloading	Know what classes are being unloaded
-XX:MaxTenuringThreshold=n	To move an object that survives a young generation collection n times to the tenured generation. Note that the throughput collector does not use the MaxTenuringThreshold parameter.
-XX:+ DisableExplicitGC	Disable explicit GC
-XX:CMSInitiatingOccupancyFraction=<percent>	The command line flag CMS Initiating Occupancy Fraction can be used to set the level at which the collection is started.

References: same as last blog entry on gc.