[joshu]

I haven't been in the industry since 2005 or so. Even so:

And how many stock symbols are there? 5500 on NYSE, 4500 on NASDAQ.

Updates per second? CSCO had a few hundred thousand updates per day.

How is the data persisted? It is typically only logged, and not retrieved in realtime.

Unfortunately, Twitter doesn't match this problem particularly well.

Delicious, which I did write, had many similar structural issues. Tags, /network, etc.