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From "Smuts, Aaron" <aaro...@amazon.com>
Subject RE: JCS Setup Questions
Date Tue, 08 Mar 2005 02:18:22 GMT

-----Original Message-----
From: Daniel Rosenbaum [mailto:drosenbaum@yahoo.com] 
Sent: Monday, March 07, 2005 4:01 PM
To: Turbine JCS Users List
Subject: Re: JCS Setup Questions

> What does it mean to have get enabled?  Does this mean that on a
> get from the cache the first thing it will do is send a message
> to the other servers asking if anyone has that object and if so
> send it across the wire?  Assuming it is this, how much time
> would the process wait for a response before giving up and going
> to the db?  If it is a short time, then could the lateral be
> configured that if a cache entry is put on A an invalidate
> message is sent to B, and if B then asks for that entry A would
> send it, rather than going to the database?  If I understand you
> correctly this is exactly what should happen.

> As a side question, wouldn't gets be slower when getting
> something not already in the cache, because of the time it must
> wait when asking the other caches if anyone else has a copy? 
> What affect would this have on performance of an app, especially
> if many gets are performed on loading a page?

Yes, this is all fairly obvious.  This is why caching is hard.  It is mostly a series of tradeoffs.

If you have get enabled for the lateral, then it will try to get data from other laterals.
 The timeout is configurable.  I don't think this is a very good idea in many situations,
since it can flood the network when an item is not in any cache and you have lots of servers
and can slow things down if the hit ratios are low.  

Since get is so important, we have a remote cache that solves the problem  There is only one
remote place to try.  This is the big difference between JCS and the original jcache specification.
 See the site docs.  The specification only had a lateral distribution model.  

The remote server model can only scale so far.  We can cluster them, dividing the gets, but
eventually it will break down.  It is not meant for thousands of servers.  But since most
of us don't have to scale that far, this is not a problem. . . 


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