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From Randy Watler <wat...@wispertel.net>
Subject Lateral Cache removal/update merge
Date Fri, 15 Sep 2006 04:00:45 GMT
We are planning to use JCS to implement a lateral cache backed by a
RDBMS. The data set we are caching is too large to fit on any particular
node in total, but we will only need a portion of the data at any given
time and the rate of crawl is very slow compared to the data set size.
That is the good news!

Because we need to support different partial working sets for each node,
I am planning on disabling the lateral cache gets. If I understand this
correctly, I should expect puts on any given node to expire the same
element in the lateral cache nodes via a remove. Subsequent access to
the same element will be made to the RDBMS. So far so good.

While we have far more reads than writes, we still have some relatively
low intensity element updates going on in this application. While we do
not demand transactional isolation levels, it would be nice to do
something with pending updates when an object is to be removed from the
lateral cache due to a put/update on another machine.

Assuming we can detect the remove from cache using an element event, (I
am not sure which event type it would be in this case), I'd like to be
able to somehow merge the pending update with the update that was just
performed to trigger the merge. It is possible to logically merge these
updates in our application, so it is really an issue of finding a way to
load in the new version of the object and maintain access to the version
being removed so that the updates can be propagated between them.

My question is how would you best accomplish this within JCS and if it
is even possible at all. While we can live with loosing the pending
updates, it would be desirable to find a way to preserve more than we
loose!

Thanks in advance for your input,

Randy Watler



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