Developer-defined Performance Metrics

Application developers may also define performance values to be included in a SeD response to a client request. For example, a DIET SeD that provides a service to query particular databases may need to include information about which databases are currently resident in its disk cache, in order that an appropriate server be identified for each client request. To store such values, the SeD developer should first choose a unique integer identifier, referred to as the tag to denote each logical datum to be stored. Values are associated with tags using the following interface:

• int diet_est_set(estVector_t ev, int userTag, double value);

The ev parameter is the estimation vector where the value will be stored, the userTag parameter denotes the chosen tag, and value indicates the value to be associated with the tag. Tagged data are used to effect scheduling policies by defining custom server response aggregation methods, described in Section 8.3.4.