How many ipalnet servers can takepart in single cluster?

Before I start, let me say that the answer is _not_ four. There is an urban legend that the maximum cluster size is four. But I've verified in a performance lab that there is nothing magic about the number four. The real answer is much more complex.

There is no hard limit. (Or at least the hard limit is much larger than any cluster could practically be.)

Ar far as what the idea number is, the critical factor is that all of the session information for a cluster has one authoritative source (the Primary KXS). So the optimal size of the cluster of limited by the ability of the Primary KXS to manage session information.

Therefore, if your application is very session information intensive your maximum cluster size will be less than if you just use session information to store basic user information. Also, complex applications generally can scale to larger clusters than simple applications. (A complex application implies that more application processing is happening for each request, and therefore the ratio of CPU used to session requests is lower.)

This also means that the maximum size of a cluster is not a given number of machines, but instead a total amount of processing power. You could have a several dozen 1-CPU machines clustered without problems, but four 12-way E4500's might be more than your Primary KXS could handle.

You will have to experiment to determine the maximum cluster size based on your application characteristics and hardware. I'd guesstimate that your are going to be able to put 30-80 CPU's in a cluster, but that's just a ballpark figure. You can use that range as a starting point for your own testing.

708857 at 2007-6-29 9:13:23 >