From sushant.iitbhu at gmail.com  Wed Jun 28 06:08:56 2023
From: sushant.iitbhu at gmail.com (Sushant Kaushik)
Date: Wed, 28 Jun 2023 11:38:56 +0530
Subject: No Full GC on JDK 17
Message-ID: <CAEqO3yBjTOJo_V7tLBKo3b7fGhXBga_279fV5OUOYQQwokS9Aw@mail.gmail.com>

  Hi All,
I'm facing a peculiar issue where i do see a full GC intermittently but
i've not been able to figure out a deterministic way to trigger a full GC.
I need full GC so that memory is allocated back to OS, this is for k8s HPA
scale down to work.
Here is the JVM config that i'm using:

>               -Xmx9830M
>
>     -Xms3200M
>       -Xlog:gc*:file=/tmp/gc.log:time,uptime
>       -server
>       -XX:MetaspaceSize=96m
>       -XX:+UseG1GC
>       -XX:MaxGCPauseMillis=200
>       -XX:+PrintFlagsFinal
>       -XX:InitiatingHeapOccupancyPercent=100
>       -XX:+ExplicitGCInvokesConcurrent
>       -XX:G1HeapRegionSize=16
>       -XX:MinMetaspaceFreeRatio=50
>       -XX:MaxMetaspaceFreeRatio=80
>       -XX:G1PeriodicGCInterval=5000
>       -XX:G1PeriodicGCSystemLoadThreshold=10.0
>       -XX:-G1PeriodicGCInvokesConcurrent
>       -XX:+UnlockDiagnosticVMOptions
>       -XX:-G1UsePreventiveGC
>
> I've set InitiatingHeapOccupancyPercent to 100, because i don't want any
concurrent GC( i read because of concurrent GC, full GC won't be triggered).

Please help me out. TIA.
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From leo.korinth at oracle.com  Wed Jun 28 08:41:18 2023
From: leo.korinth at oracle.com (Leo Korinth)
Date: Wed, 28 Jun 2023 10:41:18 +0200
Subject: No Full GC on JDK 17
In-Reply-To: <CAEqO3yBjTOJo_V7tLBKo3b7fGhXBga_279fV5OUOYQQwokS9Aw@mail.gmail.com>
References: <CAEqO3yBjTOJo_V7tLBKo3b7fGhXBga_279fV5OUOYQQwokS9Aw@mail.gmail.com>
Message-ID: <76d439d7-1c96-4d99-2e38-6410307cca11@oracle.com>

I think it is better for you to trigger an explicit GC with System.gc() 
or using jcmd precisely when you want the heap reclamation.

At least -XX:+ExplicitGCInvokesConcurrent will work against my suggestion.

I hope this helps!

/Leo

On 28/06/2023 08:08, Sushant Kaushik wrote:
>  ? Hi All,
> I'm facing a peculiar issue where i do see a full GC intermittently but 
> i've not been able to figure out a deterministic?way to trigger a full GC.
> I need full GC so that memory is allocated back to OS, this is for k8s 
> HPA scale down to work.
> Here is the JVM config that i'm using:
> 
>      ? ? ? ? ? ? ? -Xmx9830M
> 
>          ? ? -Xms3200M
>          ? ? ? -Xlog:gc*:file=/tmp/gc.log:time,uptime
>          ? ? ? -server
>          ? ? ? -XX:MetaspaceSize=96m
>          ? ? ? -XX:+UseG1GC
>          ? ? ? -XX:MaxGCPauseMillis=200
>          ? ? ? -XX:+PrintFlagsFinal
>          ? ? ? -XX:InitiatingHeapOccupancyPercent=100
>          ? ? ? -XX:+ExplicitGCInvokesConcurrent
>          ? ? ? -XX:G1HeapRegionSize=16
>          ? ? ? -XX:MinMetaspaceFreeRatio=50
>          ? ? ? -XX:MaxMetaspaceFreeRatio=80
>          ? ? ? -XX:G1PeriodicGCInterval=5000
>          ? ? ? -XX:G1PeriodicGCSystemLoadThreshold=10.0
>          ? ? ? -XX:-G1PeriodicGCInvokesConcurrent
>          ? ? ? -XX:+UnlockDiagnosticVMOptions
>          ? ? ? -XX:-G1UsePreventiveGC
> 
> I've set InitiatingHeapOccupancyPercent to 100, because i don't want any 
> concurrent GC( i read because of concurrent GC, full GC won't be triggered).
> 
> Please help me out. TIA.
> 
> 
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