Bob Griswold of Terracotta has written a blog called "Conflicting Galactic Forces in Java" that characterizes some of the differences between scaling up and scaling out. Even though this blog is a lead-in to a plug for his clustering product, he touches on a number of interesting weaknesses in the current JVM technology. In his assessment, these weakness make scaling out a much more difficult problem then he believes that it should be.
Scaling out reflected by the move towards using many smaller machines instead of few larger ones has been a trend in computing for years. Although having many smaller machines offers both cost and scaling advantages these advantages do not come without a price. This price is doubly felt when one is using VM technology such as the Java Virtual Machine.
As Bob points out, the JVM (as well the VM for Ruby and Smalltalk) were designed to abstract away from developers much of the mundane work that is often orthogonal to the problem at hand. However that assumption breaks down once an application extends beyond the boundaries of a single virtual machine. These problems extend to singularity (needed for correctness) and identity (needed to ensure singularity).
…this works almost perfectly as long as the application runs contained within a single JVM. If the application is intended to be deployed on multiple JVM's, in other words - if it is intended to be clustered or distributed, this promise falls apart.
If writing applications that scale-out is far too difficult then is it time for the Java community to explore a JVM that extends over machine boundaries or do you see products such as those offered by Terracotta to be the answer to scale-out complexity?
Threaded replies
· Bob Griswold on Scaling up and out by Kirk Pepperdine on Wed Jan 18 11:31:48 EST 2006
· Bob Griswold on Scaling up and out by James Watson on Thu Jan 19 12:13:21 EST 2006
· That's exactly what Terracotta provides by Bob Griswold on Fri Jan 20 20:14:44 EST 2006
· Not a simple model by Cameron Purdy on Mon Jan 30 12:09:35 EST 2006
· Scale out with Akamai by Eron Wright on Wed Apr 05 16:21:42 EDT 2006
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