AW: Delete a table content
AW: Delete a table content
- Subject: AW: Delete a table content
- From: Helge Staedtler <email@hidden>
- Date: Wed, 07 Sep 2005 10:42:30 +0200
I think david is absolutely right, that it is far from trivial to understand
the nice things happening behind the scenes. This freshness explorer
application is really a very nice and helpful tool to get into this deeper.
Perhaps you want to try the following, too:
http://wocode.com/cgi-bin/WebObjects/WOCode.woa/wa/ShareCodeItem?itemId=310
its an example to demonstrate, what happens if you have two instances
writing to the same DB, and it is a try to overcome the side-effects by
change-notification using WONDER's change-notification framework. it#s a bit
tricky to setup, but this what i tried to setup as a proof-of-concept after
i dealt with changenotification some time ago.
from my experience you can go a long way in one-instance-mode, if your
application supports concurrent request-handling. but again david is right
that this will only work for a specific kind of load and it needs some
special coding discipline (e.g. locking/unlocking of EC's) to keep your
concurrent requesthandling app healthy.
sooner or later one will need e.g. a second xServe with another instance
accessing the same DB. I would be interested how many of you out there a
actually driving a setup which uses in the one or the other way
ChangeNotification or some other way as basic method to keep things fresh
across many instances.
regards,
helge
Am 06.09.2005 13:38 Uhr schrieb "David Teran" unter
<email@hidden>:
>
> Am 05.09.2005 um 17:48 schrieb Fabrice Pipart:
>
>> I think you are absolutely right.
>> I gave up the idea to change the rows with raw SQL. Loosing the
>> sync was too bad for the rest of the application and it did not
>> make sense to have to refetch all the objects !
>>
>
> Sorry, but this is just a short term solution. If you want to do it
> right, you must -always- keep in mind that the database is out of
> sync. For example because you use multiple instances, the database is
> used by other systems and such cases. IMHO its just to naiv thinking
> that there is only one WO instance and only one system accessing the
> database so best is: always keep in mind that EOF caches Database
> information and always check if you need 'fresh' data for a certain
> action. I think the biggest problem for users is the fact that EOF
> caches and that they have absolutely no idea how to deal with that
> fact. Ignoring it just because one uses only a single instance means
> a lot of refactoring when you need to add just one additional
> instance or even just one additional EOF stack in the same instance.
> So its important to know the basics about data freshness and such
> things.
>
> I know others have different opinion about that but all i can say to
> them is ' go back in sandbox and pray you never need multiple EOF
> stacks or multiple instances or multiple applications using on single
> database' because the reality is they will need the one or the other
> sooner or later ;-)
>
> There is a neat demo app called 'freshness explorer' or something
> like this on connect.apple.com for download. It was published after
> WWDC 2004 and is a good starter to understand the caching stuff from
> EOF.
>
>
> cheers, david
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