Distributed processing

For purposes of illustration, let's say that the data did in fact change very fast. How would we handle that? The standard solution here is "distributed processing."

We'd have multiple database servers, but each one would handle only a certain subset of the requests. The easiest way to picture this is to imagine that each of the swipe cards has a 32-bit serial number to identify the swipe card.

If we needed to break the database server problem down into, say, 16 sub-problems, then you could do something very simple. Look at the four least significant bits of the serial number, and then use that as a server address to determine which server should handle the request. (This assumes that the 32-bit serial numbers have an even distribution of least-significant four-bit addresses; if not, there are plenty of other hashing algorithms.) Need to break the problem into 32 "sub-problems?" Just look at the five least significant bits of the serial number, and so on.

This kind of approach is done all the time at trade shows — you'll see several registration desks. One might have "Last Name A-H," "Last Name I-P," and "Last Name Q-Z" to distribute the hoards of people into three separate streams. Depending on where you live, your local driver's license bureau may do something similar — your driver's license expires on your birthday. While there isn't necessarily a completely even distribution of birthdays over the days of the year, it does distribute the problem somewhat evenly.