G1 Region size info

[Thomas Schatzl]

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