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.