ZGC Unable to reclaim memory for long time

Sundara Mohan M m.sundar85 at gmail.com
Wed Nov 6 21:04:16 UTC 2019

To be clear "before" i was referring to my previous GC, Parallel/G1/CMS.

Here is what i was seeing
Instance1 - 8G heap,   ParallelGC, 100RPS,  200ms Latency
Instance2 - 8G heap,   ZGC,           100RPS,  600ms Latency
Instance3 - 32G heap, ZGC,           100RPS,  200ms Latency

My expectation was Instance2 should give me same result as Instance1 but
that is not the case. Instead i had to move to Instance3 setting to get
what i want.
This is just my observation and it might not be same for all workloads.

But on the other hand with ZGC my throughput increased from
*(ParallelGC)97%* to* (ZGC)99.7% *and my STW pauses have never crossed 20ms.


On Wed, Nov 6, 2019 at 12:47 PM Florian Weimer <fw at deneb.enyo.de> wrote:

> * Sundara Mohan M.:
> > Hi Per
> >    As per [1] https://wiki.openjdk.java.net/display/zgc/Main it says it
> can
> > handle  *few hundred megabytes* to multi terabytes*.*
> >
> > So my understanding was if my application is running with 8G before, with
> > ZGC and same heap also it should run without issues. So far that is not
> > the case i have to increase the heap size always to make sure it gets the
> > same latency/RPS.
> What do you mean with “before”?  Thanks.

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