GC - 垃圾回收器相关参数汇总

A5.1 Heap Layout

Option	Default value	Max Value	Description
-XX:NewSize	2Mb	< 100 GB	Controls the initial size of young generation
-XX:MaxNewSize		< 100 GB	Controls the maximum size of the young generation
-XX:SurvivorRatio	8 on windows, and 64 on Solaris	<100000	Controls the size of the eden and the survivor spaces
-Xms	5 MB	< 100 GB	Initial heap size
-Xmx	4 MB	< 100 GB	Maximum heap size
-Xmn			Size of young generation
-XX:MaxTenuringThreshold	31		Maximum number of times object is aged. Set this to 0 to enable promoteall.
-XX:PermSize	4 MB	< 10 GB	Initial size of permanent generation
-XX:MaxPermSize	64 MB	< 10 GB	Maximum size of permanent generation
-XX:NewRatio	2 for server, 8 for client on Solaris		Ratio of young generation / old generation
-XX:PretenureSizeThreshold	0		Objects size greater than this is directly allocated in the older generation
-XX:+UseISM			Use intimate shared memory (see section 16.2.6.1)
-XX:+UseMPSS			Use multiple page sizes (see section 16.2.6.1)
-XX:+UseTLAB	True on Solaris		Use thread-local object allocation
-XX:+AggressiveHeap			Use for throughput applications with lots of CPUs and memory > 256MB. Turns on various flags, uses parallel scavenge collector for young generation, turns onAdaptive SizePolicy, increase sizes of TLAB and other data structures
-XX:TargetSurvivorRatio	50	100	Desired percentage of survivor space used after a scavenge

A5.2 Parallel Copying Collector

Option	Default value	Max Value	Description
-XX:+UseParNewGC			Enables young generation parallel copying collector. Use with concurrent collector or default mark-sweep-compact collector
-XX:ParallelGCThreads	As many threads as CPUs		Controls the number of threads used for copying collection

A5.3 Concurrent Collector

Option	Default value	Max Value	Description
-XX:+UseConcMarkSweepGC			Enables old generation concurrent collection
-XX:UseCMSCompactAtFullCollection	false		Enable compaction Full GC and if full collection are occurring too frequently
-XX:CMSFullGCsBeforeCompaction	1		Parameter that affects compaction of the old generation. If at least this number of concurrent collections has not succeeded between full collection, do a compaction on full collections. If 0, always do compactions on full collections whenUseCMS Compact AtFull Collection is true
-XX:PrintCMSStatistics	0		If > 0, Print statistics about the concurrent collections. For example, the number of times the concurrent collection yield to a young generation collection and the number of cards precleaned
-XX:PrintFLSStatistics	0		If > 0, print statistics about the concurrent free lists. For example, a fragmentation parameter
-XX:PrintFLSCensus	0		if > 0, print the populations of the CMS free lists
-XX:CMSInitiatingOccupancyFraction	68%		Change the percentage when a CMS collection is started

A5.4 Parallel Scavenge Collector

Option	Default value	Max Value	Description
-XX:UseParallelGC			Enables young generation parallel scavenge collector. Works only with the default mark-sweep-compact collector. Do not use with the concurrent collector.
-XX:+UseAdaptiveSizePolicy	false		Automatically sizes the young generation and chooses an optimum survivor ratio to maximize performance.
-XX:+PrintAdaptiveSizePolicy	false		Prints information about adaptive size policy
-XX:ParallelGCThreads	As many threads as CPUs		Controls the number of threads used for copying collection

A5.5 Verbose GC options

Option	Default value	Max Value	Description
-XX:+PrintGCDetails	false		PrintGC details
-XX:+PrintGCTimeStamps	false		Adds timestamp info to GC details
-XX:+PrintHeapAtGC	false		Prints detailed GC info including heap occupancy before and after GC
-XX:+PrintTenuringDistribution	false		Prints object aging or tenuring information
-XX:+PrintHeapUsageOverTime	false		Print heap usage and capacity with timestamps
-Xloggc:filename	false		Prints GC info to a log file
-verbose:gc	false		Prints some GC info
-XX:+PrintTLAB	false		Print TLAB information