Number of Parallel GC Threads

Jon Masamitsu Jon.Masamitsu at Sun.COM
Fri Jan 23 15:54:10 UTC 2009

Tony Printezis wrote On 01/23/09 07:33,:

>First, a correction. For very large machines, we don't set the number of 
>GC threads to be the same as the CPUs (there are diminishing returns if 
>we do that). Currently, you get 1 parallel GC thread per CPU for up to 8 
>CPUs, and 5/8 after that (so for 16 CPUs you get: 8 + 5/8 x 8 = 13 GC 

This is a bit of embarassment on my part.  What you say is true
for all the collectors except UseParallelGC.  In the early jdk6's
and before,  we used all the cpu's for GC for UseParallelGC
(the default for server-class machines).  That was fixed in
jdk6 update 10 (I believe).


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