1. A method for detecting anomalies for a database system, comprising: extracting one or more workload features from a query optimizer based on a query workload; generating workload feature models for the one or more extracted workload features; extracting one or more instance features from the query optimizer based on a query instance, wherein instance feature values are obtained; applying a query instance to the workload feature models to produce a prediction value for each workload feature; and reporting one or more anomalies based on a comparison of each instance feature value with a corresponding prediction value.