IDS 200 Lecture Notes - Lecture 10: Fraud, Supply Chain, Gift Card
12 Feb 2020
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Document Summary
Hopefully, you"ve all ordered something from amazon or another, similar online operation. Behind the interface, multiple systems work together to process the order: Credit card is validated and the payment processed. Within a single transaction, the sequence of data updates must be enforced. Every process step happens as a unit. In principle, it"s bad to allow multiple users access to the same data simultaneously: However, at amazon"s rate of several hundred tps, some will necessarily overlap. When one user is using a particular thing, it is locked so that no others can use it. Applicable to data rows (objects) and fields. Two database updates u and v attempt to update rows a & U updates row a and v updates b. But, now rows a and b are locked so neither update can actually finish. Livelock happens when trying to resolve a deadlock problem perpetuates it: User requests to add a product to a cart.
