SPI_saveplan saves a passed plan (prepared by
SPI_prepare) in memory that will not be freed
SPI_finish nor by the transaction manager,
and returns a pointer to the saved plan. This gives you the
ability to reuse prepared plans in the subsequent invocations of
your procedure in the current session.
Pointer to the saved plan; NULL if unsuccessful. On error, SPI_result is set thus:
if plan is NULL or invalid
if called from an unconnected procedure
The passed-in plan is not freed, so you might wish to do
SPI_freeplan on it to avoid leaking memory
If one of the objects (a table, function, etc.) referenced by the
prepared plan is dropped or redefined, then future executions of
SPI_execute_plan may fail or return different
results than the plan initially indicates.