transactions

[Milan Mimica]

Yes I have read the whole wiki several times I think, thanks for writing
it. Magma would be virtually useless without it. I think I'll go with
staying in a transaction all the time and see where it gets me.


On 20 December 2011 03:11, Chris Muller <asqueaker at gmail.com> wrote:

> Milan, I don't know if you saw this one too,
>
>    http://wiki.squeak.org/squeak/5605
>
> which mentions staying in a transaction all the time as one of a few
> possible-strategies for committing.
>
> It used to be (a long time ago) that long transactions were a
> challenge due to getting disconnected from the server whenever there
> was too much commit-activity (by the other clients) accumulated
> against against the session.  The accumulated changes are cached in
> memory on the server so unresponsive sessions must eventually be
> trimmed.
>
> But that could be frustrating for the client because, sometimes the
> user just had to do a _lot_ of work, and so it was all the worse to
> not be able to commit that work.  The solution was to make
> transactions be able to span session connections.  Now transactions
> can be weeks long, if desired.
>
> If a session disconnects with a transaction open (e.g., save and exit
> the image -- time to board the plane), the image can be restarted and
> work inside the transaction resumed later.  When the session is
> reconnected, the users work is all still there in the image, but any
> other objects which were changed in the meantime must be refreshed to
> their current state -- so it's necessary to review.  BTW, this the
> reason there can sometimes be a pause after reconnecting a
> long-disconnected session (the refresh), but its precisely what the
> system should do -- preserve the persistent state of my saved image
> and let me commit it later, when I'm good and done.
>
> So, leaving a transaction open is now a totally viable option and can
> be a fine way to go, depending on the application.
>
>  - Chris
>
>
> On Mon, Dec 19, 2011 at 12:55 PM, Chris Muller <asqueaker at gmail.com>
> wrote:
> > In magma, #begin performs an implicit #refresh, not an implicit #abort.
> >
> > See:
> >
> >  http://wiki.squeak.org/squeak/2636
> >
> >
> >
> > On Mon, Dec 19, 2011 at 11:00 AM, Milan Mimica <milan.mimica at gmail.com>
> wrote:
> >> I have spent some time trying to use Magma properly, hoping that some
> things
> >> that weren't clear at the beginning will eventually come clear. But one
> >> thing I still don't get: transactions. I understand transaction
> semantics in
> >> RDMS, but what does it mean in magma?
> >>
> >> What is the difference between modifying an object inside and outside
> >> transaction? This two code snippets don't show any difference.
> >>
> >> session := ...
> >> model := session root model.
> >> model firstName: 'foo'.
> >> session begin.
> >> model lastName: 'bar'.
> >> session commit.
> >>
> >> session := ...
> >> model := session root model.
> >> session begin.
> >> model firstName: 'foo'.
> >> model lastName: 'bar'.
> >> session commit.
> >>
> >>
> >> They both commit both firstName and lastName properties, so I don't see
> any
> >> use of opening and ending a transaction. Couldn't there just be a commit
> >> message, so that you are always in a transaction, as that is how it
> >> apparently works?
> >>
> >>
> >> --
> >> Milan Mimica
> >> http://sparklet.sf.net
> >>
> >> _______________________________________________
> >> Magma mailing list
> >> Magma at lists.squeakfoundation.org
> >> http://lists.squeakfoundation.org/mailman/listinfo/magma
> >>
>



-- 
Milan Mimica
http://sparklet.sf.net
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