The Server Programming Interface
(SPI) gives users the
ability to run SQL queries inside user-defined
C functions.
Note: The available Procedural Languages (PL) give an alternate
means to build functions that can execute queries.
In fact, SPI is just a set of native interface functions
to simplify access to the Parser, Planner, Optimizer and Executor.
SPI also does some memory management.
To avoid misunderstanding we'll use function
to mean SPI interface functions and
procedure for user-defined C-functions
using SPI.
Procedures which use SPI are called by the
Executor. The SPI calls recursively invoke the
Executor in turn to run queries. When the Executor is invoked
recursively, it may itself call procedures which may make
SPI calls.
Note that if during execution of a query from a procedure the transaction is
aborted, then control will not be returned to your procedure. Rather, all work
will be rolled back and the server will wait for the next command from the
client. This will probably be changed in future versions.
A related restriction is the inability to execute BEGIN, END and ABORT
(transaction control statements). This will also be
changed in the future.
If successful, SPI functions return a non-negative result (either via
a returned integer value or in SPI_result global variable, as described below).
On error, a negative or NULL result will be returned.
