In Hardware is Expensive, Programmers are Cheap II I promised that I’d give an example of a case where hardware is cheap compared to designing and building a more efficient application. That post pointed out a case where a relatively small investment in program optimization would have paid itself back by dramatic hardware savings across a small number of the software vendors customers.
Here’s an example of the opposite.
Circa 2000/2001 we started hosting an ASP application running on x86 app servers with a SQL server backend. The hardware was roughly 1Ghz/1GB per app server. Web page response time was a consistent 2000ms. Each app server could handle no more than a handful of page views per second.
By 2004 or so, application utilization grew enough that the page response time and the scalability (page views per server per second) were both considered unacceptable. We did a significant amount of investigation into the application, focusing first on the database, and then on the app servers. After a week or so of data gathering, we determined that the only significant bottleneck was a call to an XSLT/XML transformation function. The details escape me – and aren’t really relevant anyway, but what I remember is that most of the page response time was buried in that library call, and that call used most of the app server CPU. Figuring out how to make the app go faster was pretty straightforward.
- The app servers were CPU bound on a single library call.
- The library wasn’t going to get re-written or optimized with any reasonable work effort. (If I remember correctly, it was a Microsoft provided library, the software developers only option would and been a major re-write).
- The servers were somewhere around 4 years old and due for a routine replacement.
- The new servers would clock 3x as fast, have better memory bandwidth and larger caches. The CPU bound library call would likely scale with processor clock speed, and if it fit in the processor cache might scale better than clock.
Conclusion: Buy hardware. In this case, two new app servers replaced four old app servers, the page response time improved dramatically, and the pages views per server per second went up enough to handle normal application growth. It was clear that throwing hardware at the problem was the simplest, cheapest way to make it go away.
In The Quarter Million Dollar Query I outlined how we attached an approximate dollar cost to a specific poorly performing query. “The developers - who are faced with having to balance impossible user requirements, short deadlines, long bug lists, and whiny hosting teams complaining about performance - likely will favor the former over the latter.”
Unless of course they have data comparing hardware, software licenses and hosting costs to their development costs. My preference is to express the operational cost of solving a performance problem in ‘programmer-salaries’ or ‘programmer-months’. Using units like that helps bridge the communication gap.
My conclusion in that post: “To properly prioritize the development work effort, some rational measurement must be made of the cost of re-working existing functionality to reduce [server or database] load verses the value of using that same work effort to add user requested features.”
Related:The Quarter Million Dollar Query
Hardware is Expensive, Programmers are Cheap
Hardware is Expensive, Programmers are Cheap II