SPI_rollback rolls back the current transaction. It is approximately equivalent to running the SQL command ROLLBACK. After the transaction is rolled back, a new transaction is automatically started using default transaction characteristics, so that the caller can continue using SPI facilities.
SPI_rollback_and_chain is the same, but the new transaction is started with the same transaction characteristics as the just finished one, like with the SQL command ROLLBACK AND CHAIN.
These functions can only be executed if the SPI connection has been set as nonatomic in the call to SPI_connect_ext.
The man page SPI_rollback_and_chain(3) is an alias of SPI_rollback(3).