Re: AW: Delete a table content
Re: AW: Delete a table content
- Subject: Re: AW: Delete a table content
- From: Kieran Kelleher <email@hidden>
- Date: Wed, 7 Sep 2005 08:58:05 -0400
Perhaps I am blind, but where exactly is the Freshness Explorer app? I
watched a demo of it by James Dempsey (Apple WO Engineer) on one of the
WWDC DVDs a few months ago.
Regards, Kieran
On Sep 7, 2005, at 4:42 AM, Helge Staedtler wrote:
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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