[zohebv]

Handling updates to 7000 user accounts per second isn't what makes it hard for twitter. It is the propagation of these updates to a gazillion followers that taxes the system. Their primary overhead is the messaging update to followers. Ashton Kutcher has 6 million followers. Sending instantaneous notifications to all those million twitter clients is what makes it a killer.

TLDR; It is not the vertices in the twitter graph but the number of edges in it that is unprecedented.

[benologist]

Unprecedented, except is it really unprecedented or are we just looking at it from the sexy social startup whatever must say graph and also disrupt angle, where everything is new and super hard and nobody has problems that have ever been solved before.

RSS strikes me as an almost identical process other than the time subscribers wait to check for new content, and there are feeds with millions of subscribers. So now the problem is reduced to doing it in a timely fashion.

This is why I wonder if they're really that immensely complicated - isn't Google doing much the same thing, and possibly even at a bigger scale at one point, with their reader and FeedBurner?

[jimbokun]

"isn't Google doing much the same thing, and possibly even at a bigger scale at one point, with their reader and FeedBurner?"

Another company with a ton of employees.

Probably not that many on the FeedBurner team itself, but a lot of people at Google working on the general problem of keeping things unreasonably responsive at massive scale.

[Splines]

This is exactly the reason why every IM network has a limit to the number of contacts that you can have. I recall reading several years ago that this was an incredibly hard problem for IM providers to solve, and AFAIK none of them have allow you to have an infinite number of contacts.