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

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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