RFR: 8256419: ZGC: Remove "Heap Used Before/After Mark/Relocation" samplers

[Per Liden]

On Mon, 23 Nov 2020 09:19:24 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> I propose that we remove the following stat samplers:
>> 
>> - Heap Used Before Mark
>> - Heap Used After
>> - Heap Used Before Relocation
>> - Heap Used After Relocation
>> 
>> The simple reason is that they aren't very useful. Looking at the heap statistics table gives a much better overview of what the heap usage has looked like.
>
> GCHeapSummary doesn't contain enough information to track the usage during the cycle. We talked offline and it might be good to add an JFR event to log the "heap table" numbers from the gc log.

Thanks for reviewing!

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PR: https://git.openjdk.java.net/jdk/pull/1239