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Re: GC for Ozone
* Falko Braeutigam <falko@smb-tec.com> [010524 12:10]:
> You don't need to handle collections separatly. They are Java objects as well.
> YOu can find all proxies (external references) from an database object (which in
> fact is a graph of simple Java objects) using reflection and nothing else.
>
> IMO the problem is not to find all external references from a database object.
> The problem is that this information is stored right _inside_ the objects
> itself, which means that you would have to activate the entire database in
> memory, when you want to build the entire graph in order to search for
> unreachlabe parts of the graph.
> So IMO the GC has to work iteratively. mark&sweep _is_ iteratively AFAIK, right?
Yes, mark&sweep can be implemented iteravly, it might also help to
implment a generational GC to break up the work into smaller bits
(statistics about age of objects/frequency of deletion from live
databases would help here). Also if we keep the "color" of each OID
external we can avoid having to load/activate each object, however
this implies adding code to every DB Object to color itself upon a
write or read (depending on model used) operation. However I assume
that this is no as big a performance problem as it is for traditional
memory GC systems since writes are quiet slow as it is and a byte more
shouldn't matter.
I'm reading up on the Reflection API now since I've never worked with
it up it looks like the Class.getCLasses() and .getFields() mehtods
are just what I was looking for to find child objects.
>
>
> >
> > P.S> If anyone happens to know if there are publications on this
> > matter I would be glad to here of them since most GC stuff I have read
> > pertained to memory only systems where IO is fairly cheap compared to
> > our case.
>
> Well, field of real research - makes it real interesting ;)
>
That's why I want to work on it :) Alwyas nice to travel unkown territory.
On a diffrent note, I am developing a controller servlet atm which
uses Ozone as its back-end and I was wondering if ExternalDatabse is
thread safe, ie, can I use a single instance of ExternalDatabase or
should I generate a new one for each request I process (since they
could be processed in parallel)?
Olaf
--
()~() Olaf Mersmann - Student of Applied Physics
(-___-) eMail: olafm@slaveone.tako.de
=='-'== web: http://kimberly.dnsalias.net/ome
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