RE: Strategies for Clearing Session Objects

[None None]

I've only really been concerned with such a thing in one instance, and that 
was because we were caching some returned ResultSets, and they could be very 
large... What I wound up doing is wrapping each ResultSet in a HashMap, and 
I had two other elements, one storing the datetime stamp the object was 
created, and another specifying how long the object shoud live... Then, on 
every subsequent request I would check those values and null out any object 
older than it's specified time to live.  It's not the most elegant solution, 
but the usage pattern of this particular application made it rather 
effective.

I also considered starting a daemon thread when the app started up that 
would periodically do cleanup chores, but I never got around to doing the 
research to see if it could gain access to the session information.  I've 
used daemon threads in a number of cases for periodic tasks when I wanted 
the tasks to be intrinsically linked to the app (i.e., started and stopped 
with it, dependant on some server resources shared with the app, etc.), but 
never for cleanup tasks like this.  My bet is it's possible, but most 
probably server-specific, so I'm not sure I'd want to do that as I hate 
being tied to any particular app server.

Another option I considered but never tried to implement that SHOULD work is 
to write custom classes that will be stored in session that extend Thread.  
Then you can have a member that tells how long it can live for, and just 
kill it in run() when it's time.  I've never done this because the idea of 
spawning all those threads sounds obviously bad, but again it comes down to 
the usage pattern of the system I suspect... If you maybe have a ResultSet 
that you want to keep reusing if it exists, but you want it to always 
refresh after five minutes for instance, and you know your not going to have 
so many concurrent sessions that the number of threads wouldn't kill you, it 
might be a good way to go.  I'm not sure what number of threads starts to be 
cause for concern, it has a lot to do obviously with server resources and 
expected system load, but this idea actually had quite a bit of appeal to 
me, it was just quicker to implement what I wound up doing (and time to 
market was the primary driver, as it usually is, and what the business wants 
and when tends to trump design work unfortunately).


From: Mike Duffy <[EMAIL PROTECTED]>
Reply-To: "Struts Users Mailing List" <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Strategies for Clearing Session Objects
Date: Wed, 26 May 2004 19:04:52 -0700 (PDT)
System performance will obviously increase if unnecessary objects are 
cleared from the session.

I'd be interested in the strategies used by members of this list to clear 
unnecessary objects from
the session.

I think the most basic solution is not to clutter the session in the first 
place, but beyond that,
please share any specific strategies that you think are useful.

Thanks.
Mike

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