Class histogram output and chopping off long thin tails

[Srinivas Ramakrishna]

OK, sounds good to me.

thanks!
-- ramki

On Mon, Nov 14, 2011 at 2:10 PM, Tony Printezis
<tony.printezis at oracle.com>wrote:

>  I'll be happy if we provided a parameter to limit the histogram output.
> But, I would personally recommend that the default value for this is
> "unbounded" for the reasons I described in my previous e-mail...
>
> Tony
>
>
> On 11/14/2011 02:37 PM, Srinivas Ramakrishna wrote:
>
>
>
> On Mon, Nov 14, 2011 at 7:13 AM, Tony Printezis <tony.printezis at oracle.com
> > wrote:
>
>>  Ramki,
>>
>> First, which version of the class histogram are you referring to? I
>> assume it's the one we generate from within the JVM which goes to the GC
>> log? If you were using jmap you could just pipe the output to head or
>> similar.
>>
>
> Right -- the former.
>
>
>>
>> Is your concern mainly to keep the class histogram output reasonably
>> compact? FWIW, and I don't know how common this scenario is, I once tracked
>> down a leak by noticing that they were 2 instances of a particular class
>> instead of 1 (I was replacing once instance with a newly-allocated one, but
>> the original one ended up being queued up for finalization and held on to a
>> lot of space). If we only dumped the top N classes I would have missed this
>> piece of information.
>>
>
> Sure. I can imagine there are cases where the skinny tail is interesting
> and indeed vital. My guess (as i indicated in the email) was that perhaps
> the
> common use case was in the top part of the histogram, and the objective as
> you stated was compactness :-)
>
>
>>
>> Maybe adding a new -XX parameter :-) to set N would be a good compromise?
>>
>
> Sure. That's what i was suggesting, plus that the default be to favor
> compactness (because of my guesstimate on how the use-cases fell in
> practice,
> a guesstimate that could be wrong since it was based on subjective
> experience rather than a survey :-)
>
> thanks!
> -- ramki
>
>
>>
>> Tony
>>
>>
>> On 11/11/2011 5:31 PM, Srinivas Ramakrishna wrote:
>>
>>
>> I am posting this to hotspot-gc-use, but the idea is that it also post to
>> -dev (but given how
>> the lists are arranged, I am posting directly to the one and not the
>> other to avoid double copies
>> to those who are in the intersection of the two kists, while covering
>> those in the union of the two).
>>
>> I've noticed recently in my use of the the class histogram feature, that
>> in typical cases I am interested
>> in the top few types of objects and not in the long thin tail. I am not
>> sure how typical my use or
>> experience is, but it would appear to me (based on my limited experience
>> of late) that if we limited
>> the histogram output to the top "N" (for say N = 40 or so) classes by
>> default, it would likely satisfy
>> 80-90% of use cases. For the remaining 10% of use cases, one would
>> provide a complete dump,
>> or a dump with more entries than available by default.
>>
>> I wanted to run this suggestion by everyone and see whether this would
>> have some traction
>> wrt such a request.
>>
>> I am guessing that this may be especially useful when dealing with very
>> large applications that
>> may have many different types of objects in the heap and might present a
>> very long thin (and in
>> many cases uninteresting) tail. (There may be other ways of restricting
>> the output, for example
>> by cutting off output below a certain population or volume threshold, but
>> simply displaying the
>> top N most voluminous or populous classes would seem to be the
>> simplest....)
>>
>> Comments?
>> -- ramki
>>
>>
>>
>>
>>  _______________________________________________
>> hotspot-gc-use mailing listhotspot-gc-use at openjdk.java.nethttp://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
>>
>>
>
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