SPI_freetuptable frees a row set
created by a prior SPI command execution function, such as
SPI_execute. Therefore, this function
is often called with the global variable SPI_tuptable as argument.
This function is useful if a SPI procedure needs to execute
multiple commands and does not want to keep the results of earlier
commands around until it ends. Note that any unfreed row sets will
be freed anyway at SPI_finish. Also,
if a subtransaction is started and then aborted within execution of
a SPI procedure, SPI automatically frees any row sets created while
the subtransaction was running.
Beginning in PostgreSQL 9.3,
SPI_freetuptable contains guard logic
to protect against duplicate deletion requests for the same row
set. In previous releases, duplicate deletions would lead to
crashes.