Distributed Lock
Distributed lock
Use cases
Efficiency: Taking a lock saves you from unnecessarily doing the same work twice (e.g. some expensive computation).
e.g. If the lock fails and two nodes end up doing the same piece of work, the result is a minor increase in cost (you end up paying 5 cents more to AWS than you otherwise would have)
e.g. SNS scenarios: A minor inconvenience (e.g. a user ends up getting the same email notification twice).
e.g. eCommerce website inventory control
Correctness: Taking a lock prevents concurrent processes from stepping on each others’ toes and messing up the state of your system. If the lock fails and two nodes concurrently work on the same piece of data, the result is a corrupted file, data loss, permanent inconsistency, the wrong dose of a drug administered to a patient, or some other serious problem.
Requirementss
Exclusive
Avoid deadlock
High available
Reentrant
Comparison
Usage example in oversell
Case 1: Subtract purchased count in program and update database to target count
Case 2: Decrement database count with purchased count
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