ParallelOldGC vs ParallelGC

[Jon Masamitsu]

Run the command

java -server -XX:+UseParallelGC -XX:+PrintCommandLineFlags -version

You should see something like

java -server -XX:+UseParallelGC -XX:+PrintCommandLineFlags -version
-XX:MaxHeapSize=536870912 -XX:+PrintCommandLineFlags -XX:+UseParallelGC
java version "1.5.0_16"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_16-b02)
Java HotSpot(TM) Server VM (build 1.5.0_16-b02, mixed mode)

Note the -XX:+UseParallelGC that is printed which indicates that the
parallel young generation collector is being used.

Then run

java -server -XX:+UseParallelOldGC -XX:+PrintCommandLineFlags -version

You should see

java -server -XX:+UseParallelOldGC -XX:+PrintCommandLineFlags -version
-XX:MaxHeapSize=536870912 -XX:+PrintCommandLineFlags -XX:+UseParallelGC 
-XX:+UseParallelOldGC
java version "1.5.0_16"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_16-b02)
Java HotSpot(TM) Server VM (build 1.5.0_16-b02, mixed mode)

Note that both -XX:+UseParallelGC and -XX:+UseParallelOldGC appear so
you should be running the parallel young generation collector and the
parallel old generation collector.

If you see something different, what platform are you running on?
Can you send a snippet of the GC log?

On 12/16/08 01:28, mbien at fh-landshut.de wrote:
> Hello everyone,
> 
> is there still a difference between both flags? In all my tests on jdk  
> 5 the VM was initialized each time with identical gc setups.
> 
> flags:
> -server -XX:+UseParallelOldGC -verbose:gc -XX:+PrintGCDetails  
> -XX:+PrintGCTimeStamps
> 
> -server -XX:+UseParalleldGC -verbose:gc -XX:+PrintGCDetails  
> -XX:+PrintGCTimeStamps
> 
> jconsol reported in both cases PS MarkSweep and PS Scavange  
> collectors. (what does PS mean?)
> 
> i always thought that ParallelGC would result in
> parallel young + serial old
> and ParrallelOldGC in
> parrallel young + parralel old gcs
> 
> best regards,
> 
> michael
> 
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