The interconnect is the networking layer of Greenplum Database. When a user connects to a database and issues a query, processes are created on each of the segments to handle the work of that query. The interconnect refers to the inter-process communication between the segments, as well as the network infrastructure on which this communication relies. The interconnect uses a standard Gigabit Ethernet switching fabric.
By default, the interconnect uses UDP (User Datagram Protocol) to send messages over the network. The Greenplum software does the additional packet verification and checking not performed by UDP, so the reliability is equivalent to TCP (Transmission Control Protocol), and the performance and scalability exceeds TCP. With TCP, Greenplum has a scalability limit of 1000 segment instances. To remove this limit, UDP is now the default protocol for the interconnect.