10. A distributed parallel processing system, comprising: a compute cluster including a plurality of nodes, each node including at least one processor; an execution provider that accesses expressions from a sequential program that is running at a first machine, the execution provider receives at least one expression specifying an extension for distributed data parallel processing in the compute cluster, the execution provider automatically generates an execution plan graph and code for vertices in the execution plan graph using the extension for distributed data parallel processing, wherein the extension is an operator specifying division of a first dataset into multiple datastreams at the compute cluster, the code for at least one of the vertices receives the first dataset and provides a second dataset having at least two datastreams included therein, the two datastreams including records from the first dataset; and an execution engine that receives the execution plan graph and the code from the execution provider and manages parallel execution of the expression in the compute cluster based on the execution plan graph and the code, wherein the execution engine distributes the code for the at least one of the vertices receiving the first dataset to one or more nodes in the compute cluster corresponding to the at least one of the vertices.
10. A distributed parallel processing system, comprising: a compute cluster including a plurality of nodes, each node including at least one processor; an execution provider that accesses expressions from a sequential program that is running at a first machine, the execution provider receives at least one expression specifying an extension for distributed data parallel processing in the compute cluster, the execution provider automatically generates an execution plan graph and code for vertices in the execution plan graph using the extension for distributed data parallel processing, wherein the extension is an operator specifying division of a first dataset into multiple datastreams at the compute cluster, the code for at least one of the vertices receives the first dataset and provides a second dataset having at least two datastreams included therein, the two datastreams including records from the first dataset; and an execution engine that receives the execution plan graph and the code from the execution provider and manages parallel execution of the expression in the compute cluster based on the execution plan graph and the code, wherein the execution engine distributes the code for the at least one of the vertices receiving the first dataset to one or more nodes in the compute cluster corresponding to the at least one of the vertices. 12. A distributed parallel processing system according to claim 10 , wherein: the execution provider accesses a first expression from the program running at the first machine, the first expression invoking a method specifying that the first dataset has been sorted; and the execution provider optimizes the execution plan graph based on the specified sorting of the first dataset.