SPI_connect opens a connection
from a procedure invocation to the SPI manager. You must 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.