RFR (S): 8195115: G1 Old Gen MemoryPool CollectionUsage.used values don't reflect mixed GC results

[mandy chung]

Thanks for the reply Paul.   Try to understand a little more on the 
specific from gc-specific memory pool you depend on.

On 1/29/18 8:27 AM, Hohensee, Paul wrote:
>
> A name change would affect Amazon’s heap monitoring, and thus I expect 
> it would affect other users as well.
>
> As long as there are gc-specific memory pools, we’re going to need to 
> be able to identify them, and right now that’s done via name.
>

MemoryPoolMXBean::getType returns "heap" memory type for GC-specific 
memory pools.  Are you using this method?  Do you use the name to build 
in specific characteristic of a memory pool (e.g. eden vs old gen)?


> All the mxbeans are identified by name, so that’s a general design 
> principle. The only way I can think of to get rid of name dependency 
> would be to figure out what abstract metrics users want to monitor and 
> implement them for all collectors. HeapUsage (instantaneous occupancy) 
> is one, CollectionUsage (long-lived occupancy) is another, both of 
> these for the entire heap, not just particular memory pools.
>

The sum of HeapUsage and CollectionUsage of all heap memory pools was 
expected to give an incorrect approximation for the entire heap usage.  
Are you seeing issue/bug with the sum result?

Mandy

> That said, imo there will always be a demand for the ability to get 
> collector and memory pool specific details, so I don’t see a way to 
> get around providing named entities.
>
> Paul
>
> *From: *mandy chung <mandy.chung at oracle.com>
> *Organization: *Oracle Corporation
> *Date: *Friday, January 26, 2018 at 2:38 PM
> *To: *"Hohensee, Paul" <hohensee at amazon.com>, Erik Helin 
> <erik.helin at oracle.com>, David Holmes <david.holmes at oracle.com>
> *Cc: *"serviceability-dev at openjdk.java.net" 
> <serviceability-dev at openjdk.java.net>, 
> "hotspot-gc-dev at openjdk.java.net" <hotspot-gc-dev at openjdk.java.net>
> *Subject: *Re: RFR (S): 8195115: G1 Old Gen MemoryPool 
> CollectionUsage.used values don't reflect mixed GC results
>
> On 1/25/18 1:04 PM, Hohensee, Paul wrote:
>
>
> > The JMX API spec doesn’t specify what the memory pool or garbage > 
> collector names are, but the current names are de-facto part of the > 
> API, so if we change the existing ones, imo a CSR should be filed.
>
> The names are implementation details but I can see how an application
> might be impacted if they depend on it.  CSR approval is not strictly
> necessary while I think filing one to document the change would be
> good.
>
> Does the name change impact any application you know of?  I'm trying to
> understand if any improvement to API is needed so that applications
> don't need to depend on the names.
>
>
> Mandy
>

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