Cloud = x86 and open source

From a high-level perspective, the basic architecture of Facebook is not that different from other high performance web services.

However, Facebook is the poster child of the new generation of Cloud applications. It's hugely popular and very interactive, and as such it requires much more scalability and availability than your average website that mostly serves up information.

The "Cloud Application" generation did not turn to the classic high-end redundant platforms with heavy Relational Database Management Systems. A combination of x86 scale-out clusters, open source websoftware, and "no SQL" is the foundation that Facebook, Twitter, Google and others build upon.

However, facebook has improved several pieces of the Open Source software puzzle to make them more suited for extreme scalability. Facebook chose PHP as its presentation layer as it is simple to learn, write, and read. However, PHP is very CPU and memory intensive.

According to Facebook’s own numbers, PHP is about 39 times slower than C++ code. Thus it was clear that Facebook had to solve this problem first. The traditional approach is to rewrite the most performance critical parts in C++ as PHP Extensions, but Facebook tried a different solution: the engineers developed HipHop, a source code transformer. Hiphop transforms the PHP source code into faster C++ code and compiles it with g++.

The next piece in the Facebook puzzle is Memcached. Memcached is an in-RAM object caching system with some very cool features. Memcached is a distributed caching system, which means a memcached cache can span many servers. The "cache" is thus in fact a collection of smaller caches. It basically recuperates unused RAM that your operating system would probably waste on less efficient file system caching. These “cache nodes” do not sync or broadcast and as a result the memory cache is very scalable.

Facebook quickly became the world's largest user of memcached and improved memcached vastly. They ported it to 64-bit, lowered TCP memory usage, distributed network processing over multiple cores (instead of one), and so on. Facebook mostly uses memcached to alleviate database load.

Facebook Technology Overview The Facebook Open Compute Servers
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  • JohanAnandtech - Thursday, November 3, 2011 - link

    It is an ATI ES 1000, that is a server/thin client chip. That chip is only 2D. I can not find the power specs, but considering that the chip does not even need a heatsink, I think this chip consumes maybe 1W in idle.
  • mczak - Thursday, November 3, 2011 - link

    ES 1000 is almost the same as radeon 7000/ve (no that's not HD 7000...) (some time in the past you could even force 3d in linux with the open-source driver though it usually did not work). The chip also has dedicated ram chip (though only 16bit wide memory interface) and I'm not sure how good the powersaving methods of it are (probably not downclocking but supporting clock gating) - not sure if it fits into 1W at idle (but certainly shouldn't be much more).
  • JohanAnandtech - Thursday, November 3, 2011 - link

    I can not find any good tech resources on the chip, but I can imagine that AMD/ATI have shrunk the chip since it's appearance in 2005. If not, and the chip does consume quite a bit, it is a bit disappointing that server vendors still use it as the videochip is used very rarely. You don't need a videochip for RDP for example.
  • mczak - Thursday, November 3, 2011 - link

    I think the possibility of this chip being shrunk since 2005 is 0%. The other question is if it was shrunk from rv100 or if it's actually the same - even if it was shrunk it probably was a well mature process like 130nm in 2005 otherwise it's 180nm.
    At 130nm (estimated below 20 million transistors) the die size would be very small already and probably wouldn't get any smaller due to i/o anyway. Most of the power draw might be due to i/o too so shrink wouldn't help there neither. It is possible though it's really below 1W (when idle).
  • Taft12 - Thursday, November 3, 2011 - link

    A shrink WOULD allow production of many more units on each wafer. Since almost every server shipped needs an ES1000 chip, demand is consistently on the order of millions per year.
  • mczak - Thursday, November 3, 2011 - link

    There's a limit how much i/o you can have for a given die size (actually the limiting factor is not area but circumference so making it rectangular sort of helps). i/o pads apparently don't shrink well hence if your chip has to have some size because you've got too many i/o pads a shrink will do nothing but make it more expensive (since smaller process nodes are generally more expensive per area).
    Being i/o bound is quite possible for some chips though I don't know if this one really is - it's got at least display outputs, 16bit memory interface, 32bit pci interface and the required power/ground pads at least.
    In any case even at 180nm the chip should be below 40mm² already hence the die size cost is probably quite low compared to packaging, cost of memory etc.
  • Penti - Saturday, November 5, 2011 - link

    It's the integrated BMC/ILO solution which also includes a GPU that would use more power then the ES1000 any how. That is also what is lacking in the simple Google / Facebook compute-node setup. They don't need that kind off management and can handle that a node goes offline.
  • haplo602 - Thursday, November 3, 2011 - link

    It seems to me that the HP server is doing as well as the Facebook ones. Considering it has more featuers (remote management, integrated graphics) and a "common" PSU.
  • JohanAnandtech - Thursday, November 3, 2011 - link

    The HP does well. However, if you don't need integrated graphics and you hardly use the BMC at all, you still end up with a server that wastes power on features you hardly use.
  • twhittet - Thursday, November 3, 2011 - link

    I would assume cost is also a major factor. Why pay for so many features you don't need? Manufacturing costs should be lower if they actually build these in bulk.

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