US Patent 9684671 Parallel streaming of external data

Methods, systems, and apparatus, including computer programs encoded on computer storage media, for streaming external data in parallel from a second distributed system to a first distributed system. One of the methods includes receiving a query that requests a join of first rows of a first table in a first distributed system with second rows of an external table, the external table representing data in a second distributed system. Each of the segment nodes communicates with a respective extension service that obtains fragments from one or more data nodes of the second distributed system according to location information for the respective fragments, and provides to the segment node a stream of data corresponding to second rows of the external table. Each of the segment nodes computes joined rows between the first rows of the first table and the stream of data corresponding to second rows of the external table.