What I'm really wondering if there's a way to get something like J2EE
session replication for the application scope. Storing data which doesn't
vary between users in session variables would not only needlessly soak up
memory, but it also has the potential to leave some (many) users with old or
bad data in the session scope if the shared information changes.
So the problem occurs (and this is why I need something like session
replication) when I'm cacheing data in the application scope which was
pulled from a db which is shared amongst several coppies of an application
installed on different servers in a cluster. Because the data changes
infrequently (and requires some massaging after being retreived from the
db), it's stored in the application scope, but when it's updated in the db
it then has to be refreshed in the application scope. If I'm using the
standard application scope for the server then the problem is that if I
delete the data or refresh the data on the machine from which the update was
made, any of the remaining servers in the cluster which have cached the data
now have outdated data and no way of knowing it's outdated.
I know that there are ways I can force the data to be refreshed on the other
machines even without being able to replicate the application scope, by
storing a list of the servers in the cluster in the db and using cfhttp to
send information to each of the clustered servers, but this is rather
obtrusive and probably slow, so I'm really hoping for a graceful
alternative. Even with something like cached queries, I normally use code
like (pseudocode):
<cflock scope="application" type="exclusive" timeout="30">
<cfparam name="application.qc.myq" type="date" default="#now()#">
<cfset variables.cachedafter = application.qc.myq>
</cflock>
<cfquery name="myq" cachedafter="#variables.cachedafter#" ...>
...
</cfquery>
This way when I know that the data has changed and I need to refresh the
query I simply set the value of the application variable to Now() as in:
<cflock scope="application" type="exclusive" timeout="30">
<cfset application.qc.myq = now()>
</cflock>
And viola -- the cached query is refreshed. The problem is that if this
application is in a cluster, again, the only way to update the cachedafter
value on all of the servers in the cluster without something similar to J2EE
session replication is to write a rather complex and probably slow
sub-application to handle application data across the cluster.
> On Monday, Mar 24, 2003, at 18:58 US/Pacific, Jim Davis
> wrote:
>>> Yes, since you can use J2EE session variables and
>>> leverage the
>>> scalability of the underlying J2EE system.
>> So how does this actually work across a cluster?
> See my blog:
> http://www.corfield.org/blog/archives/2003_01.html#000055
> and the immediately preceding few articles on how to set
> it all up!
> Sean A Corfield -- http://www.corfield.org/blog/
> "If you're not annoying somebody, you're not really
> alive."
> -- Margaret Atwood
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s. isaac dealey 954-776-0046
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