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Re: GC for Ozone
On Thu, 24 May 2001, Olaf Mersmann wrote:
>
> * 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)?
ExternalDatabase is designed to be used in multi threaded environments.
(thread safe, connection pooling, connection multiplexing)
Falko
--
______________________________________________________________________
Falko Braeutigam mailto:falko@smb-tec.com
SMB GmbH http://www.smb-tec.com