SPI_rollback, SPI_rollback_and_chain — abort the current transaction
void SPI_rollback(void)
void SPI_rollback_and_chain(void)
   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.