Abstract: In general, one aspect of the subject matter described in this specification is embodied in operations of processing sequence data by selecting a distribution key according to a type of one or more tasks to be performed on the data. The key is one or more data fields of a sequence data file, e.g., a sequence alignment/map (SAM) format or binary sequence alignment/map (BAM) format file, or derived from one or more data fields of a sequence data file. The sequence data is then distributed to multiple nodes of a parallel processing relational database system. The system performs the tasks of processing the sequence data by executing database queries. The system executes the database queries on multiple nodes in parallel. The system can use query optimization functions built into the database to expedite performance of each task.