G1 parallel old gen collection

Vitaly Davidovich vitalyd at gmail.com
Tue Oct 4 20:01:32 UTC 2016

On Tue, Oct 4, 2016 at 3:37 PM, Christian Thalinger <cthalinger at twitter.com>

> First, I apologize if I get all the terminology wrong.  You know me… this
> is all a blackbox to me.
> I’m currently trying to run some Twitter services with G1 and the results
> are encouraging but not good enough.  One issue is that full GCs take much
> longer than with ParallelOld (3-4x longer).
As Charlie says, you really want to avoid Full GCs in G1 - they're super
slow, and are really a last resort.  They're not intended to be part of
normal operation.

I've seen them occur when concurrent marking is either started too late or
concurrent marking loses the race with java mutators.  There are several
ways to mitigate this, but as Charlie said, you'll need to provide more
info Chris.

> Tony said that G1’s old collection is not parallel.
> Is that still the case in JDK 9?  If yes, is someone at Oracle working on
> parallelizing it?
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