Shibboleth Developers

["Scott Cantor" <>]

> I was wondering if anyone has thought of implementing a plugin that
> would store the SP session cache on a cluster of memcache (http://
> www.danga.com/memcached/) servers?

I looked at it briefly and didn't really understand it very well, but
I was evaluating it from the perspective of using it as a default, which
also makes the additional dependency a problem. As an add-on, that's a
different story.

It also wasn't clear how well it handled writes, and my cache has to be
updateable, at least in the future.

> I guess some users would be instantly logged out if a server went
> down but that doesn't seem too bad. Memcache is normaly used in front
> of a DB but in this case it can be used independently.

It would have to be or there'd be no advantage. For timeouts to work, every
request has to update a last access timestamp, so you have to hit the actual
backing store.

Looking at it again briefly, the immediate problem I see is that my API is
implemented in terms of the exact record expiration time, not "seconds until
removal". There are specific reasons for that in order to handle inactivity
timeout without actually updating the XML data record on every request. I
need to know when the last access was, and I use the expiration to simulate
that.

I think it could be worked around, but probably by using multiple internal
records to store the last access value separately. The storage API doesn't
know or care how the data is managed, it just has to rely on the semantics
being correct, including record versioning to detect when data is out of
sync.

I have no time to do this, and I can't really tell you that the API will
allow for it unless somebody tries it, so it's pretty much down to that. I'm
happy to make adjustments within reason if they will be needed.

-- Scott