Guaranteed Delivery (GD) is a delivery mechanism that ensures that data continues to be processed from a stream to an adapter even if the Server fails, the destination (third-party server) fails, or the destination does not respond for a period of time.
Input adapters support GD using facilities provided by the source. Output adapters support GD by using Persistent Subscribe Pattern (PSP).
PSP involves a combination of an input window, a control window (also known as a truncate window), and a Flex operator with a log store. The input window on which PSP is enabled enters data into the Flex operator. The Flex operator generates a sequence number and opcode from the data and places them at the beginning of each row of data. The Flex operator then sends this data to the adapter that is attached to it. The adapter passes the information to the control window. Finally, the control window informs the Flex operator of the data that has been processed by the adapter, and the Flex operator removes this data from the log store.
