Re: caching: Session state or Application state...

<spacehopper_man@xxxxxxxxx> wrote in message
news:1133218879.717974.319780@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> I'm considering ditching all use of Session state in favour of
> Application state.
>
> This is because - from what I can work out - it will be more memory
> efficient for me.

If your only sharing data at an application scope, and need no session
independence it makes sense! Thats a judgement call on your part. Be aware
that overloading any of the state objects can be a bad thing.

> I have three questions:
>
> 1) When is memory used for Session State freed (or essentially freed)?
> - if ever...

When the session ends and the systems decides that all objects now out of
scope can be freed and garbage collected, I dont recall there being a fixed
duration as to when this happens. When the garbage collector decides that
sufficient garbage has accumulated that it is efficient to do so, it
performs a collection to free some memory.

> 2) When is memory used in Application State (or essentially freed) - eg
> - if my cache item expires due to it reaching it's expiration time - is
> it freed immediately - or must the process wait for some cleanup job to
> run.

When a cached object expires, the ASP.NET process removes it behind the
scenes immediately unless an active request for that cache item is
different to the retrieved value at request time and it needs to be updated,
then it updates the object if its priority is high enouigh to merit keeping
it cached. However, the type of cahcing and the expiration policy can see
the cache object reacting in different ways, for example if your using
sliding expiration, or SQL cache invalidation. If you keep adding items
to the cache and it gets full (ie. the free cache memory is exhausted),
ASP.NET will automatically invalidate and removes the oldest, least used, or
lowest priority items from the cache, hence you may not see your object
behave as predictably as you think it might. You need to be aware of this
if your going to use it heavily. Its worth having a read of Alex Homes
excellent article on this:
http://www.devx.com/dotnet/Article/27865/1954?pf=true


> 3) does anyone know of any docs/articles on when *exactly* memory is
> made available when using the various caching techniques?

Not exactly, this is an easy read though and you can deduce when the memory
would be freed. Only tip I guess is to watch perfromance monitor to see
exactly whats happening.

http://msdn.microsoft.com/asp.net/archive/?pull=/library/en-us/dnvs05/html/cachingnt2.asp

also read about GC here

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnpag/html/scalenetchapt05.asp


> cheers very much,
> Oli.
>


--
Regards

John Timney
ASP.NET MVP
Microsoft Regional Director


.

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