I would like to start a series of articles examining query execution paths in a distributed environment. In general, an execution path (or execution plan) is an ordered set of steps used to execute an SQL statement. Queries, in particular, are interesting because of their variety and complexity (people often speak of query plans). In a distributed system, data is spread over a number of databases and therefore collecting and processing data from multiple sources is required. In such an environment, it is vital for the database to choose an efficient execution path. The impact of choosing a sub-optimal execution path is slower responses and more resource utilization manifesting as performance degradation.