SPI_connect opens a connection to the Postgres backend. You should call this function if you will need to execute queries. Some utility SPI functions may be called from un-connected procedures.
If your procedure is already connected, SPI_connect will return an SPI_ERROR_CONNECT error. Note that this may happen if a procedure which has called SPI_connect directly calls another procedure which itself calls SPI_connect. While recursive calls to the SPI manager are permitted when an SPI query invokes another function which uses SPI, directly nested calls to SPI_connect and SPI_finish are forbidden.
SPI_connect performs the following:
Initializes the SPI internal structures for query execution and memory management.