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

[Per Liden]

On Tue, 17 Nov 2020 07:06:27 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.
>
> The ZStateSamples are reported through JFR (if the events are turned on). Is there something else that reports the heap usage to JFR recordings?

@stefank Yes, we send heap usage (GCHeapSummary events) before and after the GC cycle.

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