SPI_commit commits the current transaction. It is approximately equivalent to running the SQL command COMMIT. After the transaction is committed, a new transaction is automatically started using default transaction characteristics, so that the caller can continue using SPI facilities. If there is a failure during commit, the current transaction is instead rolled back and a new transaction is started, after which the error is thrown in the usual way.
SPI_commit_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 COMMIT 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_commit_and_chain(3) is an alias of SPI_commit(3).