SPI_execp(plan, values, nulls, tcount)
SPI_execp stores a plan prepared by SPI_prepare in safe memory protected from freeing by SPI_finish or the transaction manager.
In the current version of Postgres there is no ability to store prepared plans in the system catalog and fetch them from there for execution. This will be implemented in future versions. As a work arround, there is the ability to reuse prepared plans in the consequent invocations of your procedure in the current session. Use SPI_execp to execute this saved plan.
If nulls is NULL then SPI_execp assumes that all values (if any) are NOT NULL.
Note: If one of the objects (a relation, function, etc.) referenced by the prepared plan is dropped during your session (by your backend or another process) then the results of SPI_execp for this plan will be unpredictable.