Garbage collector and GC optimization parameters
Young Generation：Serial ParNew ParallelScavenge
Tenured Generation：CMS Parallel Old Serial Old(MSC)
Serial：
Features: Cenozoic single-threaded STW can cooperate with CMS replication algorithm
Applicable to Client mode with fewer CPUs
ParNew：
Features: Cenozoic multi-threaded STW can cooperate with CMS replication algorithm
It is suitable for Server mode with multiple CPUs , but it may not perform as well as the Serial collector under four cores .
Parallel Scavenge：
Features: Adaptive adjustment strategy throughput control STW new generation multi-threaded replication algorithm
* Throughput is the proportion of the total time of running user code. Total time = user code time + GC consumption time
Suitable for environments with a high proportion of background operations
Serial Old：
Features: Old age single-threaded mark - tidying algorithm CMS backing collector
Applicable to Client mode with fewer CPUs
Parallel Old：
Features: Multi-threaded mark - sorting algorithm throughput control
Suitable for environments where CPU resource allocation is tight and throughput needs to be controlled
CMS：
Features: fast response mark - sweep algorithm multi-threaded concurrent work
* Because the garbage collection is performed concurrently with the user thread, the old age data generated during collection cannot be recycled, and it cannot be recycled when the old age is fully loaded. It needs to be recycled in advance to reserve a certain space for the user thread.
* If the memory allocated by the old generation is insufficient or the threshold is set too low, the collection threshold may be frequently hit, resulting in performance degradation
* If the space required by the user thread is insufficient, it will cause ConcurrentMode Failure , thus switching to the backup collector Serial Old
Suitable for environments with multiple CPUs and enough memory
G1：
Features: Concurrency + parallel work predictable collection time model retains the concept of generational efficient
Suitable for multi- CPU environments
Choose a garbage collector:
UseSerialGC uses Serial+Serial Old / Client mode by default
UseParNewGCUse ParNew +SerialOld
UseConcMarkSweepGC uses ParNew+CMS+Serial Old ( as CMS backup )
UseParallelGC 使用Parallel Scavenge + Serial Old(PS MarkSweep)
UseParallelOldGC 使用Parallel Scavenge + Parallel Old
Unstable optimization parameters:
The ratio of Eden to Survivor in the new generation of SurvivorRatio
Objects whose space occupied by PretenureSizeThreshold is larger than this parameter enter the old age directly
MaxTenuringThreshold sets the age limit for promoting the old generation / Minor GC age in each new generation +1
UseAdaptiveSizePolicy with auto-sizing policy /Parallel Scavenge is effective
Does HandlePromotionFailure allow guaranteed allocation failures
ParallelGCThreads sets the number of threads for ParallelGC
GCTimeRatio The ratio of GC to total time / Parallel Scavenge effective default 99
MaxGCPauseMillis GC maximum pause time / Parallel Scavenge valid
CMSInitiatingOccupancyFraction Old age collection threshold / CMS valid
UseCMSCompactAtFullCollection does one defrag /CMS work after garbage collection is done
CMSFullGCsBeforeCompaction One defragmentation after several garbage collections / CMS is valid