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Facebook Chat Architecture (Erlang)

106 points| alifaziz | 15 years ago |docs.google.com | reply

48 comments

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[+] cageface|15 years ago|reply
The nature of contemporary web applications seems to be getting closer and closer to Erlang's original problem domain: lots of clients, continuously pulling down small updates, with a need for consistent and low latency. Maybe it's finally Erlang's turn to shine?
[+] admp|15 years ago|reply
For those who are perfectly comfortable with viewing PDFs directly, here's a link: www.erlang-factory.com/upload/presentations/31/EugeneLetuchy-ErlangatFacebook.pdf
[+] metabrew|15 years ago|reply
Interesting to see that they mention loving the hot code reloading/upgrades, but also that they don't use the OTP release/upgrade functionality.

I wonder what their process is.. Just coping over new .beams and loading them is fine for functional changes only, but you need a system to run code-upgrade hooks if you want to change the state being passed around.

[+] mononcqc|15 years ago|reply
As far as I know, you don't need releases and upgrade functionality to make use of the code-upgrade hooks. It simply works without them.

Releases and upgrades do make it simpler to synchronize what needs to be taken down in what order, restarted, left alone, etc. But simple updates are still doable without that.

[+] metabrew|15 years ago|reply
Just watched the video of the talk, "the reason we didn't use the otp release process is that the documentation was very obscure at the time..".
[+] JonnieCache|15 years ago|reply
On page 13 they quote peak inbound traffic as 1gb/second.

Would this be a gigabit or gigabyte? Usually I would just assume gigabit but in the case of facebook i dont feel so hasty...

[+] nivertech|15 years ago|reply
I guess it's Gb (Gigabit). Since the only traffic Facebook Chat has is presence, which is handled using separate C++ servers. Out of 500M users (350M active users) not many of them use chat, maybe because by design it feels disconnected from the rest of the site.
[+] DrJosiah|15 years ago|reply
I wonder if FB would be willing to post some of their load numbers...

Like... how many sessions are created per day, persisted from day to day, how many messages sent per chat session, how long windows stay open, how many restores, etc.

[+] koski|15 years ago|reply
I wonder how much it has changed since the April 2009.
[+] Aloisius|15 years ago|reply
I'm confused as to why one would build a service in a language that is so difficult to hire engineers for.
[+] SkyMarshal|15 years ago|reply
You don't have to hire engineers with N years of experience in Erlang, rather hire great engineers who are programming language polyglots, and even if they don't already know Erlang they'll get up to speed on it fast, as well as any other new and useful language that comes along.
[+] tgriesser|15 years ago|reply
It makes sense if building a service in that language means that you need to hire far fewer engineers to maintain because it is much better suited to handle the particular demands of that application, as erlang seems to be in this case
[+] iregdtoreply|15 years ago|reply
Interesting. I didn't know they used Erlang. Still, the quality of Facebook chat is pretty poor.
[+] mcs|15 years ago|reply
I wonder if they have been experimenting with Node.JS.
[+] kennu|15 years ago|reply
Node.js is nice for evented I/O, but does it solve any of the other problems Erlang is good at, such as distributed parallel processing? How do you scale a Node.js-based service horizontally over many servers?
[+] axod|15 years ago|reply
You could write facebook chat in pretty much any half decent language. The question is how competent the developers are rather than what tool they decide to use.

It's not rocket science, it's mainly plumbing - moving data around.