Mark Gritter (markgritter) wrote,
Mark Gritter
markgritter

A brick-and-mortar distributed systems problem

On Friday we climbed to the top of the Witch's Hat Water Tower. It's an old water tower (preserved as a area landmark and historic place) whose observation deck is only open once a year.

The top of the tower is reached via an internal spiral staircase which is rather narrow. The tower guides had arranged a system for tracking the number of people in the tower--- they handed blue notecards to those going up and retrieved them from those exiting the tower, thereby limiting the occupancy. But, this still led to congestion on the stairs as groups traveling in opposite directions had to squeeze by each other. Is it possible to come up with a system which also limits the number of people using the staircase in opposite directions? Without cheating by giving the guides mobile phones to communicate. :)

Time-based multiplexing is a common technique. Allow upward traffic for 5 minutes, then downward traffic for the next five minutes.

The token-based approach could also be expanded in a couple ways. For example, use two colors of tokens. Allow a group of people to start upwards but give the last person in the group a special red token. Block all other ascending traffic until the red token returns. When the red token gets to the top, collect it from the carrier and permit a group to begin going downwards, again giving the red token to the last person waiting to go down.

Now, there may be some psychological issues here where people might not appreciate being told to wait to leave the tower! But the guide was already doing a rough-and-ready contention control on the top portion of the stairs.
Tags: distributed systems, geek, minneapolis
Subscribe
  • Post a new comment

    Error

    default userpic

    Your reply will be screened

    Your IP address will be recorded 

    When you submit the form an invisible reCAPTCHA check will be performed.
    You must follow the Privacy Policy and Google Terms of use.
  • 1 comment