JDK-6362677 : Change parallel GC collector default number of parallel GC threads.
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The parallel GC collector by default uses a number of parallel GC threads that is
equal to the number of cpu's. That is too large a number on systems with more
that 8 cpu's.
The number of GC threads for hardware threads > 8
will be in most cases
8 + (n - 8) * 5/8
where n is the number of hardware threads. The
exception is for Niagara2 and later CMT machines
where it is
8 + (n - 8) * 5/16
For use by Solaris, there are two workarounds.
One is to use the client vm, for which the default is the serial collector, which,
as the name implies, is single-threaded. Use '-client'.
The other is to specify the serial collector on the command line, vis.
The default to the number of parallel GC threads should be made if
performance is not adversely affected.