Concurrent heap monitoring

[Chris Plummer]

Adding hotspot-gc-dev.

On 5/21/22 12:49 AM, Volker Simonis wrote:
> This sounds very interesting. Does this feature work with every GC or  
> does the implementation depend on specific GCs (and if the latter, 
> which GCs does your prototype currently support).
>
> Kemper, William <kemperw at amazon.com> schrieb am Fr., 20. Mai 2022, 23:46:
>
>     Taking a heap dump is a stop the world event. Garbage collection
>     events can provide heap utilization information only after a cycle
>     completes. We've found that detailed heap occupancy data (such as
>     heap inspections provide) are too expensive to use for production
>     monitoring.  Similarly, we find that heap statistics generated
>     from collection cycles may come too late and may not provide
>     enough detail (young collections do not reflect the state of the
>     old generation). We have developed a /prototype/ feature to
>     provide detailed heap metrics /concurrently//, without barriers./
>     It therefore provides only an estimate as changes to the object
>     graph may cause it to miss objects. We would like to hear the
>     thoughts of serviceability experts on such a thing. It is only at
>     the proof of concept phase, but it is able to run popular
>     benchmarks (specjbb, dacapo) with minimal overhead and the
>     estimates are sufficiently accurate for our use cases (monitoring
>     heap and object growth rates).
>
>
>     Thank you for reading,
>
>     William
>
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