Stream 2 sends along 27 MB worth of data. It’s packaging everything Polybase needs to perform operations, including JAR files and any internal conversion work that the Polybase engine might need to translate Hadoop results into SQL Server results. For example, the sqlsort at the bottom is a DLL that performs ordering using SQL Server-style collations, as per the Polybase academic paper.
Stream 2 is responsible for almost every packet from 43 through 19811; only 479 packets in that range belonged to some other stream (19811 – 43 – 18864 – 425 = 479). We send all of this data to the data node via port 50010.
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