Fault Tolerance
in FastFetch
page 2

Power Failure in the Distribution Center

If the Distribution Center's power fails one can reasonably assume many other DC processes will also be unavailable so continued picking might not be possible in any event.  Regardless, since FastFetch hardware on carts use battery power, only bay light modules will fail as a result of a widespread power failure and cart power will not be affected.  In this situation, the solution is the same as if all bay controllers fail and picking can continue as described above.  If the SQL database server and RF network use uninterruptible power supplies, power failure will have no negative consequences; otherwise, FastFetch picking can continue as described below.  

Failure of the RF (Wi-Fi) Network

If the RF network fails during picking, the FastFetch PDA or Tabet PC will not be able to communicate the results of picking to the host SQL database server, and consequently, not to the Optimizer PC.  Because the PDA or Tabet PC holds all the information required for picking, it can continue to operate in an uninterrupted manner until RF communication has been restored - at which time the PDA's or Tabet PC's SQL database will automatically be synchronized with the host SQL database server.  If the RF network fails before the PDA or Tabet PC gets a batch of orders, or if it fails during picking and is not restored after picking has been completed, the PDA or Tabet PC can be removed from the vehicle dock on the cart and placed in a desktop dock connected to the Optimizer (or another) PC.  This PC, running a FastFetch utility program, will automatically download picking data to the PDA or Tabet PC (if the failure were before picking) or upload picking results data from the PDA or Tabet PC (if the failure were during or after picking).  As a response to this source of failure, FastFetch again employs a "fail soft" solution.

Failure of the PDA or Tabet PC

Failure of the PDA or Tabet PC will obviously be detected by the picker at some point before or during the picking process.  In this case the picker will replace the failed PDA or Tabet PC with another PDA or Tabet PC and start the application.  When given a option to "download new orders" or "resume picking", the picker will choose "resume picking".  The picker will then be instructed (with voice) to scan the bar codes on cart cases and cart locations adjacent to those cases (alternately scanning each).  The scanned information will enable the PDA or Tabet PC to retrieve picking information from the host SQL database server and determine which items were picked and which items remain unpicked so picking can resume at the point of PDA or Tabet PC failure.  Scanning the cart location bar codes will enable the PDA or Tabet PC to determine where the cases are located on the cart and consequently determine which light modules to illuminate to designate order boxes into which products should be placed.  As before, FastFetch addresses PDA or Tabet PC failure problems with a "fail soft" solution.

Failure of the Optimizer PC

The Optimizer PC resides on the same local area network (LAN) as the database server and file server holding the FastFetch application programs. If the Optimizer PC fails then a spare PC (even a cheap laptop) can be attached to the LAN and the FastFetch programs can be run from the file server.   As before, FastFetch addresses Optimizer PC failure problems with a "fail soft" solution.

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