问题
I'm tuning the JVM of Java 8 and I'm trying to know what the value was defined for the parameter -XX:ParallelGCThreads. The documentation says:
-XX:ParallelGCThreads: Sets the number of threads used during parallel phases of the garbage collectors. The default value varies with the platform on which the JVM is running.
I would like to know what value was defined in my platform and if I need to change that. I don't have in this environment a JDK, only JRE.
回答1:
Default value :
java -XX:+PrintFlagsFinal | grep ParallelGCThreads
uint ParallelGCThreads = 4
If you have a running process jinfo <processId>, if it's not present in the output, it is using the default value (look under VM Flags)
回答2:
Consider the default is a fixed number N, as in -XX:ParallelGCThreads=<N>
As per the documentation, that number is based on the amount of HW threads your system has:
On a machine with N hardware threads where N is greater than 8, the parallel collector uses a fixed fraction of N as the number of garbage collector threads. The fraction is approximately 5/8 for large values of N. At values of N below 8, the number used is N.
来源：https://stackoverflow.com/questions/46178181/show-the-default-value-chosen-for-xxparallelgcthreads