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 03, 2011 - link

    No. the most important rule is that the warm air of one heatsink should not enter the stream of cold air of the other. So placing them next to each other is the best way to do it, placing them serially the worst.

    Placing them further apart will not accomplish much IMHO. most of the heat is drawn away to the back of the server, the heatsinks do not get very hot. You also lower the airspeed between the heatsinks.
    Reply
  • harrkev - Thursday, November 03, 2011 - link

    You should look again at the sine-wave plots. Power factor has more to do with the phase of the current and not so much how much like a sine-wave it looks like.

    As an example, a purely capacitive or purely inductive load will have a perfect sine wave current (but completely out of phase with the voltage), but have a power factor very close to zero...

    So, those graphs do not really tell us much unless you actually crank the numbers to calculate the real power factor.

    http://en.wikipedia.org/wiki/Power_factor#Non-line...
    Reply
  • ezekiel68 - Thursday, November 03, 2011 - link

    On page 2:

    "The next piece in the Facebook puzzle is that the Open Source tools are Memcached."

    In fact, the tools are not memchached. Instead, software objects from the PHP/c++ stack, programmed by the engineers, are stored in Memcached. Side note - those in the know pronounce it "mem-cache-dee", emphasizing with the last syllable that it is a network daemon. (similar to how the DNS server "bind" is pronounced "bin-dee") So the next piece is Memcached, but the tools are not 'memcached'.
    Reply
  • JohanAnandtech - Thursday, November 03, 2011 - link

    That is something that went wrong in the final editing by Jarred. Sorry about that and I feel bad about dragging Jarred into this, but unfortunately that is what happened. As you can see further, "Facebook mostly uses memcached to alleviate database load", I was not under the impression that the "Open Source tools are Memcached. " :-) Reply
  • ezekiel68 - Thursday, November 03, 2011 - link

    I was pretty sure it was a mistake and I only mentioned it to have the blemish removed - I've been following and admiring your technical writing since the the early 2000s. Please keep on bringing us great server architecture pieces. Don't worry about Jarred, he's fine too. We all make mistakes. Reply
  • Dug - Thursday, November 03, 2011 - link

    I'm curious what the cost would be on the servers compared to something like the HP. Reply
  • Lucian Armasu - Thursday, November 03, 2011 - link

    According to SemiAccurate, Facebook is considering Calxeda's recently announced ARM servers, too. It could be a lot more efficient to run something like Facebook on those types of servers. Reply
  • JohanAnandtech - Thursday, November 03, 2011 - link

    I personally doubt that very much. The memcached servers are hardly CPU intensive, but a 32 bit ARM processor will not fit the bill. Even when ARM will get 64 bit, it is safe to say that x86 will offer much more DIMM slots. It remains to be seen how the ratio Watt/ RAM cache will be. Until 64 bit ARMs arrive with quite a few memory channels: no go IMHO.

    And the processing intensive parts of the facebook architecture are going to be very slow on the ARMs.

    The funny thing about the ARM presentations is that they assume that virtualization does not exist in the x86 world. A 24 thread x86 CPU with 128 GB can maybe run 30-60 VMs on it, lowering the cost to something like 5-10W per VM. A 5W ARM server is probably not even capable of running one of those machines at a decent speed. You'll be faced with serious management overhead to deal with 30x more servers (or worse!), high response times (single thread performance take a huge dive!) just to save a bit on the power bill.

    As a general rule: if the Atom based servers have not made it to the shortlist yet, they sure are not going to replace it by ARM based ones.
    Reply
  • tspacie - Thursday, November 03, 2011 - link

    The FaceBook servers take a higher line voltage for increased efficiency. What voltage was supplied to the HP server for these tests? Reply
  • JohanAnandtech - Thursday, November 03, 2011 - link

    Both servers used 230V. I have added this to benchmark page (Thanks, good question). So in reality the Facebook server can consume slightly less. Reply

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