SPI_saveplan man page
SPI_saveplan — save a prepared statement
SPIPlanPtr SPI_saveplan(SPIPlanPtr plan)
SPI_saveplan copies a passed statement (prepared by SPI_prepare) into memory that will not be freed by SPI_finish nor by the transaction manager, and returns a pointer to the copied statement. This gives you the ability to reuse prepared statements in the subsequent invocations of your procedure in the current session.
the prepared statement to be saved
Pointer to the copied statement; or NULL if unsuccessful. On error, SPI_result is set thus:
if plan is NULL or invalid
if called from an unconnected procedure
The originally passed-in statement is not freed, so you might wish to do SPI_freeplan on it to avoid leaking memory until SPI_finish.
In most cases, SPI_keepplan is preferred to this function, since it accomplishes largely the same result without needing to physically copy the prepared statement's data structures.