[lukev]

Yes, that sounds fine (and I'm aware of the Spolsky article posted in another comment.)

But the fact is that a system of that size simply must already be split up into discrete services or components. (If it's not, then that should be their first priority. But I can't imagine Facebook is running everything they do out of one process).

So they could port each service/component one at a time, rigorously testing and improving performance as they go. Then they'd not only get the benefit of a better runtime, but also a safer, faster language. In fact, if they're anything like most companies I know, they're always in the process of rewriting one service or another to improve performance or features, whether in a new language or not. All they'd need to do would be to switch to the new language whenever they were refactoring existing code anyway.

Of course I can't make the decision for them, and they are rightly hesitant to do an entire rewrite. But it seems like they're going to fairly extreme lengths to stay with PHP.

[swah]

> But the fact is that a system of that size simply must already be split up into discrete services or components.

Come on, they created Thrift, I think we can assume they use it?