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Comment by rbranson | Hacker News Reader

What this article fails to note is that writing C++ code to serve up web pages would be much less efficient from a human time perspective. You'd need many more developers working, and the average American emits 20 tons of CO2 per year. So if Facebook has 100 developers hacking PHP code, they'd probably need at least 200, or possibly 300 developers hacking C++ code. 100 developers is 2,000 tons of CO2 per year (at average rates). From an economic standpoint, it would make much more business sense to use carbon offsets. Not to mention that a 10x end-to-end efficiency improvement is AWFULLY optimistic. I'd say 2x or 3x at best.

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There's a more glaring deficiency than that, which is that CPU is rarely the bottleneck on a webserver.

A "web server" in Facebook's cluster is just Apache+PHP. It doesn't do any disk work. It's not reading anything from disk, as that gets forked over to memcached or MySQL. If you've got thousands of boxes in this arrangement, clearly reducing the CPU usage thru whatever means will get you more efficiency.

can you elaborate more on "no disk work" and forked over things? i didnt get.

The webserver will only do computations which data they get from other services (memcache, etc...). They will never fetch the data locally, so there is no local bottleneck except the local bandwith and the efficiency of the code, thus the cpu.

then only logical reasoning behind is cheap machines for webservers and very powerful ones for "data" servers. otherwise network bandwith is only a fraction cpu-storage one.

Even on a diskless machine, the limit still is not necessarily "CPU usage". The machine might be limited by I/O bandwidth -- both to the clients and to those memcached and MySQL servers. It might be limited by the amount of memory that must be dedicated to each connection or process, even while that process is sleeping on I/O (which is most of the time).

Most likely, the overhead of running a server is so large that the power consumption problem is all about saving servers, rather than saving CPU cycles. In which case these other variables are just as likely to be a big concern as the speed of your HTML template's WHILE loops.

I totally agree, which is why a 10x speedup is ludicrous. The C++ code would likely just accelerate the code to the point where it was network and/or memory bound. I think a 2-3x improvement is warranted given all of the things I know about the Facebook architecture.

But American's who would code in C++ already exist and are emitting CO2 regardless of what they are doing. As long as there is unemployment, there would be no net gain in CO2 by switching to C++.

One could argue that any resource Facebook was using, human, energy, physical, or otherwise, is going to get consumed in some form regardless. What the article focuses on is Facebook's operation itself, not the net impact. Also, the unemployment rate of programmers in general is relatively very low, explaining the mean annual wage of $87,900.

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