JEP 248: Make G1 the Default Garbage Collector

Erik Österlund erik.osterlund at
Tue Jun 2 15:49:55 UTC 2015


Micro comment included belowŠ

Den 02/06/15 16:46 skrev Kirk Pepperdine <kirk.pepperdine at>:
>I¹ve moved a number of apps to G1 with good success. I¹ve seen a number
>of apps where CMS was better and I¹ve seen where there was little if any
>difference. I rarely move apps to Parallel which suggests I should be in
>full agreement with this JEP. However, I don¹t feel I have a broad enough
>experience with the G1 to understand what it would do in the general
>population. IME, you don¹t want to even consider G1 unless you¹re in a
>fairly large heap. 2G is better served with CMS or Parallel. Even 4G is
>better with CMS. If you were to say G1 for >16G or something like that,
>I¹d be less concerned.

Why are we still talking about when CMS is better than G1? Changing the
default from ParallelGC to G1 should be invariant of when CMS is better
than G1 as it would hardly lead to any current CMS users complaining,
since they already specify CMS explicitly. So should¹t we focus the
discussion only on the scope of ParallelGC vs G1? Or am I wrong?

Oh and with the risk of reading between the lines, extracting CMS from
your comment, it sounds like for heap size >4G, you would currently prefer
G1 over ParallelGC by default? In that case, can¹t we just check that
simple condition when picking GC if none is specified as I suggested
earlier, and move the constant down as G1 continues to improve? Just an
idea! :)


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