4.2 Workloads

< Free Open Study >

In order that we can model and analyze systems, we need to develop means to test and/or stress systems of interest. These means to test or stress systems are called workloads. A workload should be developed so it faithfully models the nature of the true load on the system of interest. Workloads are constructed based on the focus of the analysis. For example, if we are interested in examining the hardware of a computer system in comparison to another, our focus may be on the low-level instructions. We would need to measure the instruction mix seen on a running system and then develop a synthetic mix of instructions based on these measures. Another example is to measure transaction throughput through some database system. This workload would have transactional units of work that read and write data items from the database system and do some additional computational work mimicking the real system. The database community has developed such workloads for conventional databases, object relational databases, data warehouses, and data mining. These workloads are called TP benchmarks.

When designing a workload, it is important that we understand how the workload will load down the system of interest. It is not sufficient to simply provide a token load; the load must provide the means to stress the system being analyzed. We want workloads that will cause the measured system to go into saturation. We want to see where the system gets to 100 percent utilization of resources and to sustain such loads for some duration of time.

Once a workload is developed, we will want to use some form of distribution function to select items from our workload and to present them to the system for service. For example, if we have developed n transaction types for our database system analysis, we may wish to use a uniform distribution to select database data items for the transactions to operate on and use the exponential distribution to present transactions to the system for processing. Using these means our workload will be presented to our system in a way that mimics the real-world situation, but which we have total control over.

Workloads also need to be developed so they test the components we want them to test. For example, if we are testing the database system, a simple instruction mix workload will not provide the kind of information we are interested in. The instructions alone are not representative of the desired load: transactions. Transactions are composed of transactional boundaries, database access and alteration commands, and data manipulation commands. More on workloads will follow in later chapters.

< Free Open Study >