Re: Re: Ozone List does not work anymore...?

Hi Christian,

Yes sure, If you have not got the answers you need when i get back after next 
week I'll try to answer your questions though Leo, Wieslaw or Falko are more 
clear about the inner workings of the storage engine than I am so lets hope 
one of them can answer...

Best regards,
Per

Wednesday 06 July 2005 09.52 skrev Christian Merenda:
> Hi Per,
>
> at first I´d like to wish you a nice vacation then!
>
> For your information: I already worked with Ozone some time ago, so I have
> the practical experience. Nevertheless this time I need to know the
> concepts behind the product because they're are crucial in the context of
> my current project.
>
> So I would appreciate your help and the help of others to clear the open
> issues. Naturally I won´t bother you any more in your vacations! But I
> would be very pleased if you could dive in the open issues when you´re back
> at home.
>
> Perhaps the other core developers might help to clear the issues right
> now...?
>
> Thanks in advance,
> Christian
>
> > Hi Christian,
> >
> > Actually this mail reached the mailing list a couple of days ago. Your
> > summarizing points are basically correct.
> >
> > I'm on vacation so I will not dive into your open issues. However, best
> > way to get started with Ozone is just to start! :) Use tests frequently
> > for anything you are unsure of and you will develop empirical, first hand
> > knowledge about how it works rather than relying on my weak memory ;)
> >
> > Best regards,
> > Per
> >
> > Tuesday 05 July 2005 21.23 skrev Christian Merenda:
> > > Hi Per,
> > >
> > > there are other people who can post to the list. I just gave it a try,
> > > but it didn't work again. :(
> > >
> > > So I would be very pleased, if you could clear the points for me on a
> > > personal basis. I need to know now, because I´d like to jumpstart with
> > > Ozone, but there are several points I need to understand from the first
> > > day on.
> > >
> > > In the following I send the e-mail I´m not able to post for a few days
> > > now. I would appreciate the help of Leo and Wieslaw, too. Thanks a lot.
> > >
> > >
> > > Hello Leo, Per and Wieslaw,
> > >
> > > I know, in my last mail I asked a lot of questions. Nevertheless, the
> > > most of them were some kind of summary regarding my mailings with Per.
> > > Thanks to you, Per! Wieslaw and Leo cleared the point about the
> > > isolation level and transactional behaviour of Ozone. Thanks to you,
> > > too!
> > >
> > > Could you now write some short comments to the summary points. Are my
> > > assumptions correct? And can you clear the open issues please.
> > >
> > > SUMMARY POINTS
> > > ===============
> > >
> > > Summary Point 1:
> > > At any time there´s only one instance of a persistent object in memory.
> > > This object resides for the whole lifecycle at the server´s site. If a
> > > client invokes some method, this method-call is always (!) delegated to
> > > the server transparently. You generate some client-side stubs in a
> > > CORBA style fashion, which handle the client-server interaction.
> > >
> > > Summary Point 2:
> > > The programmer has to differentiate between read-only and update
> > > methods. Therefore you have the /* update */ statement. Whenever a
> > > read-only method is invoked, the server acquires a read lock on the
> > > corresponding object. Whenever an update method is invoked, the server
> > > acquires a write/exclusive lock. If a server-side persistent object
> > > calls other methods of potentially other persistent objects, the
> > > corresponding locks are acquired in the context of the client-side
> > > transaction.
> > >
> > > Summary Point 3:
> > > You can have multiple, concurrent readers but only one writer. If a
> > >  write-lock is granted, every transaction has to wait for the object.
> > > If a read-lock is granted, other readers are welcome, but a writer has
> > > to wait until the object is released by everybody. The locks are
> > > released at the end of a transaction. A writer may wait indefinitely,
> > > because of upcoming read-only transactions.
> > >
> > >
> > > OPEN ISSUES
> > > ===========
> > >
> > > Open Issue 1:
> > > What about timeouts?
> > >
> > > Open Issue 2:
> > > What kind of server-side cross-transactional caching strategy do you
> > > have? You place the (related) persistent objects in clusters, which are
> > > stored on disk at a size of 64 kbyte, am I right? You probably have
> > > some kind of index, so that you know, in which cluster you can find an
> > > object with a specific OID. At request time, you put the whole page in
> > > memory - the objects are instantiated.
> > >
> > > What do you do if an update occurs? Do you write to the disk
> > > immediately, or are the changes cached in memory as long as the page is
> > > written back to the disk as a whole?
> > >
> > > How do you decide whether to keep the page in memory or release it to
> > > the disk?
> > >
> > > How do you guarantee atomicity and durability of a transaction? Do you
> > > have some kind of logging engine? Something else?
> > >
> > > Open Issue 3:
> > > Do you have some kind of instance pool, so that object instantiation
> > > works faster?
> > >
> > > Best regards,
> > > Christian
> > >
> > > > I have no idea. Sometimes SourceForge is heavily loaded and it takes
> > > > several days before messages goesw through. My guess is that this is
> > > > what you are experiencing.
> > > >
> > > > Best regards,
> > > > Per
> > > >
> > > > Monday 04 July 2005 11.06 skrev Christian Merenda:
> > > > > Hello Per,
> > > > >
> > > > > I´ve tried several times now, but somehow I´m not able to post to
> > > > > the ozone-list anymore. Do you have a glue about that? What is the
> > > > > problem?
> > > > >
> > > > > Best regards,
> > > > > Christian
> >
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