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From Geoff Howard <coc...@leverageweb.com>
Subject Re: caching database generated pages / eventcache block to core?
Date Tue, 14 Oct 2003 19:28:20 GMT
Christian Haul wrote:
> On 13.Oct.2003 -- 03:02 PM, Geoff Howard wrote:
> 
>>Christian Haul wrote:
> 
>>I saw the following for a start:
>>- Config(s) for the various connections to establish and maintain.
>>- Durable subscription handling.
> 
> I think we need "at least once" semantics to avoid delivering dirty
> caches. I've seen durable connections mentioned in conjunction with
> subscribers that are offline. Cocoon shutting down would invalidate
> caches anyway (and other program state), so is this really needed?

Cocoon persists caches if configured to use persistent store (and if 
jetty is not used at least as configured in the bundled version).  So 
between that and network loss and reconnection, I've always thought 
durable subscriptions would turn out to be crucial.

Generally, I've thought the eventcache needs to be "fail fast" in the 
sense that if it encounters a condition that reveals that any events may 
have been missed the entire cache (or at least anything with Event based 
validity) needs to be invalidated.

>>- Configurable message listeners for each connection/topic/queue. In the 
>>case of EventAwareCache, this may be slightly dependent on 
>>implementation.  A more advanced system might want to push the new 
>>content out in the body of the message.  A simple one would just handle 
>>the lookup of the Cache and translating the Message to an Event.
>>
>>Most of my thinking of the JMS block is clouded by its use in eventcache 
>>but of course other uses abound and a general set of services 
>>simplifying the integration of JMS into Cocoon would probably be 
>>generally useful.
> 
> OK, I've put the sample in a new JMS block and created an action that
> could send JMS messages. There's a JMSConnection (bad name) that holds
> connection properties and instantiates a connection + session.

Ok, I'll check this out.  When I went back to look at the JMS block on 
my HDD it was much thinner than I remembered it.  I'm sure I'll be able 
to factor anything it offerred in to what you've got now.

> I haven't put the jars into the CVS because I would like to hear more
> opinions about redistribution of jms and jndi jars. BTW OpenJMS does
> distribute them.

Probably time for a separate topic on just that question, or a query on 
PMC where other Apache peeps are subscribed.

Geoff


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