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Utilization Law and Service Demand

Relationship between service time, utilization and throughput

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    Consider that you are in a bank queue behind 10 persons and estimate that the bank teller is taking around 5 minutes per customer to count currency. At queue management counter, it takes another 3 min to get token for each customer. Here 5 min and 3 min are respective service times for each counter. In all, a customer has to spend on an average 8 mins to get his order completed at the bank. This total time duration at counters to perform a customer‘s request is called Service demand at the counter per customer. It is the sum of all the service times at sequential hops for a request to be serviced. In case of a single counter to process the customer request, the service demand and service time would be the same.

    Service demand:
    In software performance engineering, the service demand is the amount of resource time required to execute a request. The time spent by a request on a given server or component such as CPU, disk is the service time for that component.

    Example of Service demand : If a request spends 0.02 Seconds on disc, the service demand for disc is 0.02 Seconds.

    Utilization Law

    Utilization law defines the relationship between service demand , utilization and Throughput.

    Utilization = Throughput * Service demand

    Utilization is measured in percentage
    Throughput in Transactions Per Seconds
    Service Demand in seconds

    Example :

    Consider a disk that is serving 40 requests/second each of which requires 0.02 second of disk service time. The utilization law tells us that the utilization of this disk is product of throughput and service demand.


    Utilization = Throughput * Service demand

    Disc Utilization = 40*0.02 =80%