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I think maintaining consistent state over all turnstiles at all stations is too complicated. It requires a large infrastructure overhead. Putting the stored val
by vecter 18y ago
I think maintaining consistent state over all turnstiles at all stations is too complicated. It requires a large infrastructure overhead. Putting the stored value on the card is much simpler and doesn't require nearly as much overhead b/c it allows each turnstile to be an independent unit that reads and writes the card.
- Retric 18y agoI don't think the data changes all that fast assume 5billion cards at 10bytes a user it's ~500MB per station. Assuming 2million transactions an hour your talking about ~40megabytes of data an hour DSL would be fast enough. Now each station would keep a local copy the Database and transmit to the 30 or so other stations as long as they send data before you can reach the next station it should work just fine. Granted 10 years ago storing value on each card would have been more useful but the turn styles should easily be able to handle the full database.
- vecter 18y agoI'm not saying it's not doable, I'm just saying it's more complicated (and probably much more expensive) than the alternative. It also makes individual turnstile failures more difficult to handle. Suppose the network died on one of the turnstiles. Then you'd have to have build a caching system that it resorts to in case of network failures to prevent giving people free rides, and a way to merge state with the rest of the network once it rejoined. Of course you can do it, but I hope you're starting to see how complexity could grow faster than one might expect. I imagine that there are better ways to solve the problem at hand (security) that don't involve adding thousands of lines of code, miles of fiber, and hundreds of thousands of dollars.