[Jboss-dev-forums] [Design of JBoss Collaboration Server] - Re: Brief statement of JBMS design goals

[lhoriman <do-...@jb...>]

This time hopefully I'll get the quote tags right :-)

"dmlloyd" wrote : anonymous wrote : Horseshit. Round-robin DNS can distribute mail delivery code across servers.
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  | Load balancing is not clustering.  The point is that you don't have to bridge state between the servers.  I could set up ten MTA boxes and load balance among them, but that's not a cluster.  If one box goes down, everything connected to it goes down too.
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Arguing about what is and isn't clustering is kinda silly.  There is obviously bridged state because the nodes share a common view of the database.  The clustered, replicated (or invalidated) cache is what gets it to scale beyond the database limitations.  It's a cluster.

An SMTP box going down is no big deal.  It may halt any transactions in progress, but clients will queue and redeliver.  There's very little point in making that part any more robust.  Mail will get to it's destination, it's just a question of when.  

"dmlloyd" wrote : 
  | If your point is that a database may not suffice for large installations, I'm with you there, although there are things you can do to mitigate that (Oracle has a cluster product, and so does MySQL, I'm sure lots of others do too).
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I have a lot of experience with Oracle RAC from the days I worked on The Sims Online.  It's not a panacea for scalability.  In fact, unless you write your application specifically anticipating the behavioral characteristics of RAC, each additional node will cause your application to de-scale pretty dramatically.

It's been my experience that for most applications, clustering the database (either through fancy software or replication) is hard and usually ineffective.  Clustering the application (through app-level in-memory caches, ie hibernate) offers the ability to scale much higher - and if you still need to, at the end of the day you can still fall back to databse federation/replication schemes as an additional step.

"dmlloyd" wrote : 
  | However it seems like the message store is the only single point of contention in the system.  I imagine that if one database isn't enough, and database clustering is not enough, you could use several databases.
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  | In a large installation though, I'd bet that the MTAs will see far more CPU activity than the message store will... once you figure in the fact that the MTA handles inbound and outbound mail, and that we've reached a fine point in the evolution of the internet where spam accounts for at least 40% of email sent to the average ISP.

Try writing a mailing list manager.  1 message in easily translates to 10,000 messages out, plus a considerable amount of processing and munging of each message.  Spam is the least of your problems :-)

Jeff Schnitzer
http://subetha.tigris.org

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