SPI_push should be called before
executing another procedure that might itself wish to use SPI.
SPI_push, SPI is no longer in
a "connected" state, and SPI function
calls will be rejected unless a fresh
SPI_connect is done. This ensures a clean
separation between your procedure's SPI state and that of another
procedure you call. After the other procedure returns, call
SPI_pop to restore access to your
own SPI state.
related functions automatically do the equivalent of
SPI_push before passing control back to the SQL
execution engine, so it is not necessary for you to worry about
this when using those functions. Only when you are directly
calling arbitrary code that might contain
SPI_connect calls do you need to issue