NYCPHP Meetup

[George Schlossnagle]

On Jul 14, 2004, at 9:27 AM, Sol wrote:

> It seems that everyone agree on the meaning of
> "scalability" but not "WHERE" and "HOW" to apply it.
> Can an expert weight in here?

To make a semantic nitpick, I would say that you can't apply 
'scalability'.  You can aply 'scalability principles'.

As far as how, that's quite beyond an email conversation.  There are 
plenty of books, papers, talks and discussions about what design 
factors contribute to scalable design.  Probably the best advice is to 
figure out what components of an architecture are unscalable (i.e. 
cannot be grown without changing their architectural design) and 
figuring out how to change them into something which can be scaled.

As far as where (or I'd say 'when') you should try to make you 
applications scalable, I guess that's up to you.  There are some folks 
who would say that you should always build your applications to be 
scalable.  I think that's definitely valid if you're building any sort 
of commercial software or software you plan to set free in the wild.  
It's much easier to build something right from the ground-up than to 
redesign it later, and apps which leave your control often have a way 
of being pulled into uses you never suspected.

As an aside, the stock definition of scalability that Hans threw out 
(which is an excellent one, imho) ignores the resource cost of scaling. 
  In general, you would prefer a solution whose cost scales linearly (or 
better yet sub-linearly, good luck there) with cost.  What this means 
is that if you are at capacity and you double your traffic, your costs 
should double as well.  There are many applications which scale, but 
not linearly (due for example to interdependencies between services).  
These apps 'scale' but become cost prohibitive.



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