EVALUATION

The information has been added to the Java SE 7u4 Release Notes as a JVM feature.
                                     

EVALUATION

http://hg.openjdk.java.net/lambda/lambda/hotspot/rev/24cae3e4cbaa
                                     

EVALUATION

http://hg.openjdk.java.net/hsx/hotspot-gc/hotspot/rev/24cae3e4cbaa
                                     

EVALUATION

After review and some discussion, went with the solution in the first entry:  if UseParallelGC is enabled, then enable UseParallelOldGC (unless it has been otherwise disabled via the command line or rc file).  Relatedly, if UseParallelOldGC is enabled, then enable UseParallelGC (this is done unconditionally, since UseParallelOldGC requires UseParallelGC).
                                     

EVALUATION

The argument-processing semantics are simple, but not completely trivial.  The current behavior is that if -XX:+UseParallelOldGC is specified on the command-line, it automatically enables -XX:+UseParallelGC (parallel young gc).  This should be preserved.  This RFE adds the behavior that when -XX:+UseParallelGC is enabled, either by ergonomics or explicitly on the command line, that -XX:+UseParallelOldGC is also enabled.

The only question is what the arg processing code should do with the command line:

    java -XX:-UseParallelOldGC -XX:+UseParallelGC ...

The relevant point is that -XX:-UseParallelOldGC occurs before -XX:+UseParallelGC.  The convention for hotspot argument processing is "last one wins" and one could  reasonably interpret -XX:+UseParallelGC as implying -XX:+UseParallelOldGC.  Doing so would cause the above command line to enable UseParallelOldGC.  While it's reasonable, it's not particularly intuitive or user friendly.  I think the best choice for the above command line would be to disable UseParallelOldGC.
                                     

EVALUATION

What I actually had in mind was for server ergo to set UseParallelOldGC, which
would set UseParallelGC automatically.  I think that if only UseParallelGC is
specified on the command line, the user should still get what he/she gets now,
which is serial old + parallel young.  If both UseParallelOldGC and
UseParallelGC are specified in any order, the same thing happens as now, which is
parallel old + parallel young.

Inother words, I think that everything should work exactly as it does now,
except that server ergo should set UseParallelOldGC rather than UseParallelGC.