https://www.postgresql.org/docs/current/spi-spi-prepare-extended.html

SUMMARY: just setup a _SPI_plan in memory

SPI_prepare_extended
	// switch to executor memory context
	_SPI_begin_call
	**_SPI_prepare_plan**
	// switch to old memory context
	_SPI_end_call

_SPI_prepare_plan
	raw_parser
	analyze_and_rewrite
	CompleteCachedPlan