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From Chris Lohfink <clohf...@apple.com>
Subject Re: G1GC CPU Spike
Date Fri, 15 Jun 2018 20:59:33 GMT
There are no bad GCs in the gclog (worse is like 100ms). Everything looks great actually from
what I see. CPU utilization isn't inherently a bad thing for what its worth.

Chris

> On Jun 14, 2018, at 1:18 PM, rajpal reddy <rajpalreddy444@gmail.com> wrote:
> 
> Hey Chris,
> 
> Sorry to bother you. Did you get a chance to look at the gclog file I sent last night.
> 
> On Wed, Jun 13, 2018, 8:44 PM rajpal reddy <rajpalreddy444@gmail.com <mailto:rajpalreddy444@gmail.com>>
wrote:
> Chris,
> 
> sorry attached wrong log file. attaching gc collection seconds and cpu. there were going
high at the same time and also attached the gc.log. grafana dashboard and gc.log timing are
4hours apart gc can be see 06/12th around 22:50
> 
> rate(jvm_gc_collection_seconds_sum{"}[5m])
> 
> > On Jun 13, 2018, at 5:26 PM, Chris Lohfink <clohfink@apple.com <mailto:clohfink@apple.com>>
wrote:
> > 
> > There are not even a 100ms GC pause in that, are you certain theres a problem?
> > 
> >> On Jun 13, 2018, at 3:00 PM, rajpal reddy <rajpalreddy444@gmail.com <mailto:rajpalreddy444@gmail.com>>
wrote:
> >> 
> >> Thanks Chris I did attached the gc logs already. reattaching them now<gc.log.1.current>.
> >> 
> >> it started yesterday around 11:54PM 
> >>> On Jun 13, 2018, at 3:56 PM, Chris Lohfink <clohfink@apple.com <mailto:clohfink@apple.com>>
wrote:
> >>> 
> >>>> What is the criteria for picking up the value for G1ReservePercent?
> >>> 
> >>> 
> >>> it depends on the object allocation rate vs the size of the heap. Cassandra
ideally would be sub 500-600mb/s allocations but it can spike pretty high with something like
reading a wide partition or repair streaming which might exceed what the g1 ygcs tenuring
and timing is prepared for from previous steady rate. Giving it a bigger buffer is a nice
safety net for allocation spikes.
> >>> 
> >>>> is the HEAP_NEWSIZE is required only for CMS
> >>> 
> >>> 
> >>> it should only set Xmn with that if using CMS, with G1 it should be ignored
or else yes it would be bad to set Xmn. Giving the gc logs will give the results of all the
bash scripts along with details of whats happening so its your best option if you want help
to share that.
> >>> 
> >>> Chris
> >>> 
> >>>> On Jun 13, 2018, at 12:17 PM, Subroto Barua <sbarua116@yahoo.com.INVALID>
wrote:
> >>>> 
> >>>> Chris,
> >>>> What is the criteria for picking up the value for G1ReservePercent?
> >>>> 
> >>>> Subroto 
> >>>> 
> >>>>> On Jun 13, 2018, at 6:52 AM, Chris Lohfink <clohfink@apple.com
<mailto:clohfink@apple.com>> wrote:
> >>>>> 
> >>>>> G1ReservePercent
> >>>> 
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> >> 
> >> 
> >> 
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> 


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