JEP 248: Make G1 the Default Garbage Collector

Stefan Johansson stefan.johansson at
Fri Jun 5 12:12:25 UTC 2015

On 2015-06-05 00:08, mark.reinhold at wrote:
> 2015/6/4 6:44 -0700, charlie.hunt at
>> Wanted to come back to this thread, continue the dialog, reiterate the
>> objective, (try to) summarize the concerns and put forth a potential
>> plan for this JEP going forward.
>> Intent: Use G1 GC as the default collector chosen by the JVM when no
>> GC is explicitly set at the JVM command line.
>> ...
> Charlie -- thanks for the excellent summary of this wide-ranging
> discussion!
>> ...
>> Suggested plan for moving forward:
>> - Make G1 the default collector in JDK 9, continue to evaluate G1 and
>>    enhance G1 in JDK 9
>> - Mitigate risk by reverting back to Parallel GC before JDK 9 goes
>>    “Generally Available” (Sept 22, 2016 [1]) if warranted by continuing
>>    to monitor observations and experiences with G1 in both JDK 9
>>    pre-releases and latest JDK 8 update releases
>> - Address enhancing ergonomics for selecting a default GC as a
>>    separate JEP if future observations suggests its needed
> I think this is a fine plan.
> Stefan -- To move forward with JEP 248, could you please revise the
> second item in the "Risks and Assumptions" section to note that there
> is some concern that G1 might not be ready to become the default, that
> making it the default now will allow us to get more feedback on it, and
> that if it proves to be not ready then we'll revert the default to the
> Parallel GC in time for JDK 9 GA?
Mark, I've extended second item as follows:
   - G1 is seen as a robust and well-tested collector. It is not expected
     to have stability problems, but becoming the default collector will
     increase its visibility and may reveal previously-unknown issues. If
     a critical issue is found that can't be addressed in the JDK 9 time
     frame, we will revert back to use Parallel GC as the default for the
     JDK 9 GA.


> Ben -- Can you live with this plan?
> - Mark

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