SPI_rollback — abort the current transaction
void SPI_rollback(void)
   SPI_rollback rolls back the current transaction.  It
   is approximately equivalent to running the SQL
   command ROLLBACK.  After a transaction is rolled back, a
   new transaction has to be started
   using SPI_start_transaction before further database
   actions can be executed.
  
   This function can only be executed if the SPI connection has been set as
   nonatomic in the call to SPI_connect_ext.