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From "Craig R. McClanahan" <craig...@apache.org>
Subject Re: Addition of 'dirty' field to Session interface
Date Thu, 09 Aug 2001 19:40:30 GMT


On Thu, 9 Aug 2001, Kief Morris wrote:

> Craig R. McClanahan typed the following on 12:57 PM 8/8/2001 -0700
> >> Another possibility would be to flag the session is dirty when getAttribute()
> >> is called - it would result in unnecessary saves since it assumes the 
> >attribute
> >> was modified even when it wasn't, but it would be safer.
> >
> >Someone has told me (haven't confirmed personally) that some app servers
> >treat a setAttribute() -- as opposed to getAttribute() -- as the signal to
> >set the internal "dirty" flag.  The idea is that, if your application
> >modifies the internal state of an existing session attribute, then you
> >should call session.setAttribute() again to notify the container.
> 
> Yes, flagging the session is dirty on setAttribute() makes sense. I was
> thinking that by also flagging it on getAttribute(), you're depending less
> on developers to take an extra step (calling setDirty() or making another
> call to setAttribute()). If an attribute is retrieved from the session, it may 
> have been modified, so make the assumption that it was just to be safe.
> But this could erase a lot of the benefit of the dirty flag optimization, since
> writes are typically more common than reads. 
> 
> Now that I think about it though, any time a session is used in a request, its 
> lastAccessedTime will be updated, so the session must be considered dirty.
> So worrying about tracking attributes isn't necessary: the session only needs
> to be flagged dirty when it is retrieved. Tracking the dirty status is still a good 
> optimization, since it ensures sessions aren't saved multiple times between 
> requests, or after requests which never access the session.
> 

If I knew that the access time had been updated but not any attributes, I
could probably distribute that information pretty cheaply (without having
to serialize and deserialize the attributes as well).  Thus, it's probably
worth distinguishing between the two cases.

> Vishy, what do you think?
> 
> Kief
> 
> 

Craig



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