G1 Region size info

[Gopal, Prasanna CWK]

Hi Thomas

Thanks for your reply. We have following G1 configuration at the moment 


-Xmx7G 
 -Xms7G 
 -XX:+UseG1GC 
 -XX:+UnlockExperimentalVMOptions 
 -XX:InitiatingHeapOccupancyPercent=60 
 -XX:G1ReservePercent=20 
 -XX:G1ReservePercent=20 
-XX:G1HeapRegionSize=32M
 -XX:G1MixedGCLiveThresholdPercent=85   
 -XX:MaxGCPauseMillis=500 
 -XX:+ParallelRefProcEnabled  
 -XX:+PrintAdaptiveSizePolicy  
 -XX:+PrintHeapAtGC  
 -XX:+PrintReferenceGC   
 -XX:+PrintGCDateStamps 
 -XX:+PrintTenuringDistribution 
 -XX:+PrintGCApplicationConcurrentTime 
 -XX:+PrintGCApplicationStoppedTime 
 
Apart from these parameters, can we try another parameter to make the evacuation more aggressive? 


-XX:G1MixedGCLiveThresholdPercent=85   
-XX:InitiatingHeapOccupancyPercent=60 ==> we have experimented with less values , it is just making the concurrent cycle without claiming any significant. 
-XX:MaxGCPauseMillis=500

Our object allocation rate is very high, before increasing the memory can we try any other parameter which can make the evacuation more aggressive? Appreciate your help. Please do let me know, if you need any more information. 

Regards
Prasanna


-----Original Message-----
From: Thomas Schatzl [mailto:thomas.schatzl at oracle.com] 
Sent: 08 February 2017 16:13
To: Gopal, Prasanna CWK <prasanna.gopal at blackrock.com>; hotspot-gc-use at openjdk.java.net
Subject: Re: G1 Region size info

Hi,

On Wed, 2017-02-08 at 12:25 +0000, Gopal, Prasanna CWK wrote:
> Hi All
>  
> I am trying to understand the region size info provided in of our 
> application’s GC log file.
>  
> We are running an application with the following configuration
>  
> -Xmx7G

[...]

>  
> Does this mean,  our heap occupancy is only 352 MB after Post-Sorting 
> phase ?. It doesn’t co-relate with the information provided at thd end 
> of GC clean up phase (4283M->4121M(6144M), 0.0066530 secs) , which say 
> the heap size is 4121M.

Post-sorting only considers regions that are collection set candidates
- i.e. regions that G1 will clean out in the next reclamation phase.
I.e. contain lots of garbage.

If you think that is too little (g1 not cleaning out enough in mixed gcs), you might want to make evacuation more aggressive.

From the post-marking snippet it seems though that there are not many regions with lots of garbage there anyway though.

Post-marking statistics is what you want to look at and compare with.

Thanks,
  Thomas



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