Class histogram output and chopping off long thin tails

[Srinivas Ramakrishna]

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
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