Entire heap size = young generation + old generation + persistent generation
normal management parameters
-server
-Xmx2g -- maximum available memory
-Xms2g -- initialize heap size
-Xmn256m --newSize The
persistent generation is generally fixed in size of 64m, so increase the young After generation, the old generation size will be reduced. This value has a great impact on system performance. Sun officially recommends setting the stack size of each thread to be 3/8 of the entire heap.
-XX:PermSize=128m
-Xss256k .
After JDK5.0, the stack size of each thread is 1M, and the previous stack size of each thread is 256K. Adjust the memory size required by the threads of the application. In the same physical memory, reducing this value can generate more threads. However, the operating system still has a limit on the number of threads in a process, which cannot be generated indefinitely, and the experience value is around 3000~5000.
-XX:+DisableExplicitGC prohibits calling System.gc(); but the gc of the jvm is still valid
-XX:+UseConcMarkSweepGC uses the concurrent mark-swap algorithm for GC for the old generation
-XX:+CMSParallelRemarkEnabled whether to enable parallelism
-XX:+UseCMSCompactAtFullCollection to open the pair Old generation compression. May affect performance, but can eliminate fragmentation
-XX:LargePageSizeInBytes=128m Set large page size for Java heap
-XX:+UseFastAccessorMethods Optimize getter method performance for primitive types
-XX:+UseCMSInitiatingOccupancyOnly
CMS has a dynamic checking mechanism.
Based on historical records, CMS predicts how long it will take for the old age to fill up and how long it will take to recycle.
CMS can automatically perform garbage collection based on its own predictions before the old generation space runs out.
This feature can be turned off with the parameter UseCMSInitiatingOccupancyOnly.
-XX:CMSInitiatingOccupancyFraction=70 CMS generation occupancy percentage to start CMS collection cycle
- is a standard parameter, all vm implementations must be functions that implement these parameters, and backward
-X is a non-standard parameter, all JVMs implement these parameters by default, but it is not guaranteed that all JVM implementations are satisfied, and backwards are not guaranteed Compatible with
-XX non-Stable parameters, such parameters will be different for each jvm implementation and may be canceled at any time in the future