SPI The Server Programming Interface (SPI) gives writers of user-defined C functions the ability to run SQL commands inside their functions. SPI is a set of interface functions to simplify access to the parser, planner, and executor. SPI also does some memory management. The available procedural languages provide various means to execute SQL commands from procedures. Most of these facilities are based on SPI, so this documentation might be of use for users of those languages as well. To avoid misunderstanding we'll use the term function when we speak of SPI interface functions and procedure for a user-defined C-function that is using SPI. Note that if a command invoked via SPI fails, then control will not be returned to your procedure. Rather, the transaction or subtransaction in which your procedure executes will be rolled back. (This might seem surprising given that the SPI functions mostly have documented error-return conventions. Those conventions only apply for errors detected within the SPI functions themselves, however.) It is possible to recover control after an error by establishing your own subtransaction surrounding SPI calls that might fail. This is not currently documented because the mechanisms required are still in flux. SPI functions return a nonnegative result on success (either via a returned integer value or in the global variable SPI_result, as described below). On error, a negative result or NULL will be returned. Source code files that use SPI must include the header file executor/spi.h. SPI_connect 3 SPI_connect connect a procedure to the SPI manager SPI_connect int SPI_connect(void) SPI_connect opens a connection from a procedure invocation to the SPI manager. You must call this function if you want to execute commands through SPI. Some utility SPI functions can be called from unconnected procedures. If your procedure is already connected, SPI_connect will return the error code SPI_ERROR_CONNECT. This could happen if a procedure that has called SPI_connect directly calls another procedure that calls SPI_connect. While recursive calls to the SPI manager are permitted when an SQL command called through SPI invokes another function that uses SPI, directly nested calls to SPI_connect and SPI_finish are forbidden. (But see SPI_push and SPI_pop.) SPI_OK_CONNECT on success SPI_ERROR_CONNECT on error SPI_finish 3 SPI_finish disconnect a procedure from the SPI manager SPI_finish int SPI_finish(void) SPI_finish closes an existing connection to the SPI manager. You must call this function after completing the SPI operations needed during your procedure's current invocation. You do not need to worry about making this happen, however, if you abort the transaction via elog(ERROR). In that case SPI will clean itself up automatically. If SPI_finish is called without having a valid connection, it will return SPI_ERROR_UNCONNECTED. There is no fundamental problem with this; it means that the SPI manager has nothing to do. SPI_OK_FINISH if properly disconnected SPI_ERROR_UNCONNECTED if called from an unconnected procedure SPI_push 3 SPI_push push SPI stack to allow recursive SPI usage SPI_push void SPI_push(void) SPI_push should be called before executing another procedure that might itself wish to use SPI. After SPI_push, SPI is no longer in a connected state, and SPI function calls will be rejected unless a fresh SPI_connect is done. This ensures a clean separation between your procedure's SPI state and that of another procedure you call. After the other procedure returns, call SPI_pop to restore access to your own SPI state. Note that SPI_execute and related functions automatically do the equivalent of SPI_push before passing control back to the SQL execution engine, so it is not necessary for you to worry about this when using those functions. Only when you are directly calling arbitrary code that might contain SPI_connect calls do you need to issue SPI_push and SPI_pop. SPI_pop 3 SPI_pop pop SPI stack to return from recursive SPI usage SPI_pop void SPI_pop(void) SPI_pop pops the previous environment from the SPI call stack. See SPI_push. SPI_execute 3 SPI_execute execute a command SPI_execute int SPI_execute(const char * command, bool read_only, long count) SPI_execute executes the specified SQL command for count rows. If read_only is true, the command must be read-only, and execution overhead is somewhat reduced. This function can only be called from a connected procedure. If count is zero then the command is executed for all rows that it applies to. If count is greater than 0, then the number of rows for which the command will be executed is restricted (much like a LIMIT clause). For example: SPI_execute("INSERT INTO foo SELECT * FROM bar", false, 5); will allow at most 5 rows to be inserted into the table. You can pass multiple commands in one string, but later commands cannot depend on the creation of objects earlier in the string, because the whole string will be parsed and planned before execution begins. SPI_execute returns the result for the command executed last. The count limit applies to each command separately, but it is not applied to hidden commands generated by rules. When read_only is false, SPI_execute increments the command counter and computes a new snapshot before executing each command in the string. The snapshot does not actually change if the current transaction isolation level is SERIALIZABLE, but in READ COMMITTED mode the snapshot update allows each command to see the results of newly committed transactions from other sessions. This is essential for consistent behavior when the commands are modifying the database. When read_only is true, SPI_execute does not update either the snapshot or the command counter, and it allows only plain SELECT commands to appear in the command string. The commands are executed using the snapshot previously established for the surrounding query. This execution mode is somewhat faster than the read/write mode due to eliminating per-command overhead. It also allows genuinely stable functions to be built: since successive executions will all use the same snapshot, there will be no change in the results. It is generally unwise to mix read-only and read-write commands within a single function using SPI; that could result in very confusing behavior, since the read-only queries would not see the results of any database updates done by the read-write queries. The actual number of rows for which the (last) command was executed is returned in the global variable SPI_processed. If the return value of the function is SPI_OK_SELECT, SPI_OK_INSERT_RETURNING, SPI_OK_DELETE_RETURNING, or SPI_OK_UPDATE_RETURNING, then you can use the global pointer SPITupleTable *SPI_tuptable to access the result rows. Some utility commands (such as EXPLAIN) also return row sets, and SPI_tuptable will contain the result in these cases too. The structure SPITupleTable is defined thus: typedef struct { MemoryContext tuptabcxt; /* memory context of result table */ uint32 alloced; /* number of alloced vals */ uint32 free; /* number of free vals */ TupleDesc tupdesc; /* row descriptor */ HeapTuple *vals; /* rows */ } SPITupleTable; vals is an array of pointers to rows. (The number of valid entries is given by SPI_processed.) tupdesc is a row descriptor which you can pass to SPI functions dealing with rows. tuptabcxt, alloced, and free are internal fields not intended for use by SPI callers. SPI_finish frees all SPITupleTables allocated during the current procedure. You can free a particular result table earlier, if you are done with it, by calling SPI_freetuptable. const char * command string containing command to execute bool read_only true for read-only execution long count maximum number of rows to process or return If the execution of the command was successful then one of the following (nonnegative) values will be returned: SPI_OK_SELECT if a SELECT (but not SELECT INTO) was executed SPI_OK_SELINTO if a SELECT INTO was executed SPI_OK_INSERT if an INSERT was executed SPI_OK_DELETE if a DELETE was executed SPI_OK_UPDATE if an UPDATE was executed SPI_OK_INSERT_RETURNING if an INSERT RETURNING was executed SPI_OK_DELETE_RETURNING if a DELETE RETURNING was executed SPI_OK_UPDATE_RETURNING if an UPDATE RETURNING was executed SPI_OK_UTILITY if a utility command (e.g., CREATE TABLE) was executed SPI_OK_REWRITTEN if the command was rewritten into another kind of command (e.g., UPDATE became an INSERT) by a rule. On error, one of the following negative values is returned: SPI_ERROR_ARGUMENT if command is NULL or count is less than 0 SPI_ERROR_COPY if COPY TO stdout or COPY FROM stdin was attempted SPI_ERROR_TRANSACTION if a transaction manipulation command was attempted (BEGIN, COMMIT, ROLLBACK, SAVEPOINT, PREPARE TRANSACTION, COMMIT PREPARED, ROLLBACK PREPARED, or any variant thereof) SPI_ERROR_OPUNKNOWN if the command type is unknown (shouldn't happen) SPI_ERROR_UNCONNECTED if called from an unconnected procedure The functions SPI_execute, SPI_exec, SPI_execute_plan, and SPI_execp change both SPI_processed and SPI_tuptable (just the pointer, not the contents of the structure). Save these two global variables into local procedure variables if you need to access the result table of SPI_execute or a related function across later calls. SPI_exec 3 SPI_exec execute a read/write command SPI_exec int SPI_exec(const char * command, long count) SPI_exec is the same as SPI_execute, with the latter's read_only parameter always taken as false. const char * command string containing command to execute long count maximum number of rows to process or return See SPI_execute. SPI_execute_with_args 3 SPI_execute_with_args execute a command with out-of-line parameters SPI_execute_with_args int SPI_execute_with_args(const char *command, int nargs, Oid *argtypes, Datum *values, const char *nulls, bool read_only, long count) SPI_execute_with_args executes a command that might include references to externally supplied parameters. The command text refers to a parameter as $n, and the call specifies data types and values for each such symbol. read_only and count have the same interpretation as in SPI_execute. The main advantage of this routine compared to SPI_execute is that data values can be inserted into the command without tedious quoting/escaping, and thus with much less risk of SQL-injection attacks. Similar results can be achieved with SPI_prepare followed by SPI_execute_plan; however, when using this function the query plan is customized to the specific parameter values provided. For one-time query execution, this function should be preferred. If the same command is to be executed with many different parameters, either method might be faster, depending on the cost of re-planning versus the benefit of custom plans. const char * command command string int nargs number of input parameters ($1, $2, etc.) Oid * argtypes an array containing the OIDs of the data types of the parameters Datum * values an array of actual parameter values const char * nulls an array describing which parameters are null If nulls is NULL then SPI_execute_with_args assumes that no parameters are null. bool read_only true for read-only execution long count maximum number of rows to process or return The return value is the same as for SPI_execute. SPI_processed and SPI_tuptable are set as in SPI_execute if successful. SPI_prepare 3 SPI_prepare prepare a plan for a command, without executing it yet SPI_prepare SPIPlanPtr SPI_prepare(const char * command, int nargs, Oid * argtypes) SPI_prepare creates and returns an execution plan for the specified command but doesn't execute the command. This function should only be called from a connected procedure. When the same or a similar command is to be executed repeatedly, it might be advantageous to perform the planning only once. SPI_prepare converts a command string into an execution plan that can be executed repeatedly using SPI_execute_plan. A prepared command can be generalized by writing parameters ($1, $2, etc.) in place of what would be constants in a normal command. The actual values of the parameters are then specified when SPI_execute_plan is called. This allows the prepared command to be used over a wider range of situations than would be possible without parameters. The plan returned by SPI_prepare can be used only in the current invocation of the procedure, since SPI_finish frees memory allocated for a plan. But a plan can be saved for longer using the function SPI_saveplan. const char * command command string int nargs number of input parameters ($1, $2, etc.) Oid * argtypes pointer to an array containing the OIDs of the data types of the parameters SPI_prepare returns a non-null pointer to an execution plan. On error, NULL will be returned, and SPI_result will be set to one of the same error codes used by SPI_execute, except that it is set to SPI_ERROR_ARGUMENT if command is NULL, or if nargs is less than 0, or if nargs is greater than 0 and argtypes is NULL. SPIPlanPtr is declared as a pointer to an opaque struct type in spi.h. It is unwise to try to access its contents directly, as that makes your code much more likely to break in future revisions of PostgreSQL. There is a disadvantage to using parameters: since the planner does not know the values that will be supplied for the parameters, it might make worse planning choices than it would make for a normal command with all constants visible. SPI_prepare_cursor 3 SPI_prepare_cursor prepare a plan for a command, without executing it yet SPI_prepare_cursor SPIPlanPtr SPI_prepare_cursor(const char * command, int nargs, Oid * argtypes, int cursorOptions) SPI_prepare_cursor is identical to SPI_prepare, except that it also allows specification of the planner's cursor options parameter. This is a bitmask having the values shown in nodes/parsenodes.h for the options field of DeclareCursorStmt. SPI_prepare always takes these options as zero. const char * command command string int nargs number of input parameters ($1, $2, etc.) Oid * argtypes pointer to an array containing the OIDs of the data types of the parameters int cursorOptions integer bitmask of cursor options; zero produces default behavior SPI_prepare_cursor has the same return conventions as SPI_prepare. Useful bits to set in cursorOptions include CURSOR_OPT_SCROLL, CURSOR_OPT_NO_SCROLL, and CURSOR_OPT_FAST_PLAN. Note in particular that CURSOR_OPT_HOLD is ignored. SPI_getargcount 3 SPI_getargcount return the number of arguments needed by a plan prepared by SPI_prepare SPI_getargcount int SPI_getargcount(SPIPlanPtr plan) SPI_getargcount returns the number of arguments needed to execute a plan prepared by SPI_prepare. SPIPlanPtr plan execution plan (returned by SPI_prepare) The count of expected arguments for the plan. If the plan is NULL or invalid, SPI_result is set to SPI_ERROR_ARGUMENT and -1 is returned. SPI_getargtypeid 3 SPI_getargtypeid return the data type OID for an argument of a plan prepared by SPI_prepare SPI_getargtypeid Oid SPI_getargtypeid(SPIPlanPtr plan, int argIndex) SPI_getargtypeid returns the OID representing the type id for the argIndex'th argument of a plan prepared by SPI_prepare. First argument is at index zero. SPIPlanPtr plan execution plan (returned by SPI_prepare) int argIndex zero based index of the argument The type id of the argument at the given index. If the plan is NULL or invalid, or argIndex is less than 0 or not less than the number of arguments declared for the plan, SPI_result is set to SPI_ERROR_ARGUMENT and InvalidOid is returned. SPI_is_cursor_plan 3 SPI_is_cursor_plan return true if a plan prepared by SPI_prepare can be used with SPI_cursor_open SPI_is_cursor_plan bool SPI_is_cursor_plan(SPIPlanPtr plan) SPI_is_cursor_plan returns true if a plan prepared by SPI_prepare can be passed as an argument to SPI_cursor_open, or false if that is not the case. The criteria are that the plan represents one single command and that this command returns tuples to the caller; for example, SELECT is allowed unless it contains an INTO clause, and UPDATE is allowed only if it contains a RETURNING clause. SPIPlanPtr plan execution plan (returned by SPI_prepare) true or false to indicate if the plan can produce a cursor or not, with SPI_result set to zero. If it is not possible to determine the answer (for example, if the plan is NULL or invalid, or if called when not connected to SPI), then SPI_result is set to a suitable error code and false is returned. SPI_execute_plan 3 SPI_execute_plan execute a plan prepared by SPI_prepare SPI_execute_plan int SPI_execute_plan(SPIPlanPtr plan, Datum * values, const char * nulls, bool read_only, long count) SPI_execute_plan executes a plan prepared by SPI_prepare. read_only and count have the same interpretation as in SPI_execute. SPIPlanPtr plan execution plan (returned by SPI_prepare) Datum * values An array of actual parameter values. Must have same length as the plan's number of arguments. const char * nulls An array describing which parameters are null. Must have same length as the plan's number of arguments. n indicates a null value (entry in values will be ignored); a space indicates a nonnull value (entry in values is valid). If nulls is NULL then SPI_execute_plan assumes that no parameters are null. bool read_only true for read-only execution long count maximum number of rows to process or return The return value is the same as for SPI_execute, with the following additional possible error (negative) results: SPI_ERROR_ARGUMENT if plan is NULL or invalid, or count is less than 0 SPI_ERROR_PARAM if values is NULL and plan was prepared with some parameters SPI_processed and SPI_tuptable are set as in SPI_execute if successful. If one of the objects (a table, function, etc.) referenced by the prepared plan is dropped during the session then the result of SPI_execute_plan for this plan will be unpredictable. SPI_execp 3 SPI_execp execute a plan in read/write mode SPI_execp int SPI_execp(SPIPlanPtr plan, Datum * values, const char * nulls, long count) SPI_execp is the same as SPI_execute_plan, with the latter's read_only parameter always taken as false. SPIPlanPtr plan execution plan (returned by SPI_prepare) Datum * values An array of actual parameter values. Must have same length as the plan's number of arguments. const char * nulls An array describing which parameters are null. Must have same length as the plan's number of arguments. n indicates a null value (entry in values will be ignored); a space indicates a nonnull value (entry in values is valid). If nulls is NULL then SPI_execp assumes that no parameters are null. long count maximum number of rows to process or return See SPI_execute_plan. SPI_processed and SPI_tuptable are set as in SPI_execute if successful. SPI_cursor_open 3 SPI_cursor_open set up a cursor using a plan created with SPI_prepare SPI_cursor_open Portal SPI_cursor_open(const char * name, SPIPlanPtr plan, Datum * values, const char * nulls, bool read_only) SPI_cursor_open sets up a cursor (internally, a portal) that will execute a plan prepared by SPI_prepare. The parameters have the same meanings as the corresponding parameters to SPI_execute_plan. Using a cursor instead of executing the plan directly has two benefits. First, the result rows can be retrieved a few at a time, avoiding memory overrun for queries that return many rows. Second, a portal can outlive the current procedure (it can, in fact, live to the end of the current transaction). Returning the portal name to the procedure's caller provides a way of returning a row set as result. The passed-in data will be copied into the cursor's portal, so it can be freed while the cursor still exists. const char * name name for portal, or NULL to let the system select a name SPIPlanPtr plan execution plan (returned by SPI_prepare) Datum * values An array of actual parameter values. Must have same length as the plan's number of arguments. const char * nulls An array describing which parameters are null. Must have same length as the plan's number of arguments. n indicates a null value (entry in values will be ignored); a space indicates a nonnull value (entry in values is valid). If nulls is NULL then SPI_cursor_open assumes that no parameters are null. bool read_only true for read-only execution Pointer to portal containing the cursor. Note there is no error return convention; any error will be reported via elog. SPI_cursor_open_with_args 3 SPI_cursor_open_with_args set up a cursor using a query and parameters SPI_cursor_open_with_args Portal SPI_cursor_open_with_args(const char *name, const char *command, int nargs, Oid *argtypes, Datum *values, const char *nulls, bool read_only, int cursorOptions) SPI_cursor_open_with_args sets up a cursor (internally, a portal) that will execute the specified query. Most of the parameters have the same meanings as the corresponding parameters to SPI_prepare_cursor and SPI_cursor_open. For one-time query execution, this function should be preferred over SPI_prepare_cursor followed by SPI_cursor_open. If the same command is to be executed with many different parameters, either method might be faster, depending on the cost of re-planning versus the benefit of custom plans. The passed-in data will be copied into the cursor's portal, so it can be freed while the cursor still exists. const char * name name for portal, or NULL to let the system select a name const char * command command string int nargs number of input parameters ($1, $2, etc.) Oid * argtypes an array containing the OIDs of the data types of the parameters Datum * values an array of actual parameter values const char * nulls an array describing which parameters are null If nulls is NULL then SPI_cursor_open_with_args assumes that no parameters are null. bool read_only true for read-only execution int cursorOptions integer bitmask of cursor options; zero produces default behavior Pointer to portal containing the cursor. Note there is no error return convention; any error will be reported via elog. SPI_cursor_find 3 SPI_cursor_find find an existing cursor by name SPI_cursor_find Portal SPI_cursor_find(const char * name) SPI_cursor_find finds an existing portal by name. This is primarily useful to resolve a cursor name returned as text by some other function. const char * name name of the portal pointer to the portal with the specified name, or NULL if none was found SPI_cursor_fetch 3 SPI_cursor_fetch fetch some rows from a cursor SPI_cursor_fetch void SPI_cursor_fetch(Portal portal, bool forward, long count) SPI_cursor_fetch fetches some rows from a cursor. This is equivalent to a subset of the SQL command FETCH (see SPI_scroll_cursor_fetch for more functionality). Portal portal portal containing the cursor bool forward true for fetch forward, false for fetch backward long count maximum number of rows to fetch SPI_processed and SPI_tuptable are set as in SPI_execute if successful. Fetching backward may fail if the cursor's plan was not created with the CURSOR_OPT_SCROLL option. SPI_cursor_move 3 SPI_cursor_move move a cursor SPI_cursor_move void SPI_cursor_move(Portal portal, bool forward, long count) SPI_cursor_move skips over some number of rows in a cursor. This is equivalent to a subset of the SQL command MOVE (see SPI_scroll_cursor_move for more functionality). Portal portal portal containing the cursor bool forward true for move forward, false for move backward long count maximum number of rows to move Moving backward may fail if the cursor's plan was not created with the CURSOR_OPT_SCROLL option. SPI_scroll_cursor_fetch 3 SPI_scroll_cursor_fetch fetch some rows from a cursor SPI_scroll_cursor_fetch void SPI_scroll_cursor_fetch(Portal portal, FetchDirection direction, long count) SPI_scroll_cursor_fetch fetches some rows from a cursor. This is equivalent to the SQL command FETCH. Portal portal portal containing the cursor FetchDirection direction one of FETCH_FORWARD, FETCH_BACKWARD, FETCH_ABSOLUTE or FETCH_RELATIVE long count number of rows to fetch for FETCH_FORWARD or FETCH_BACKWARD; absolute row number to fetch for FETCH_ABSOLUTE; or relative row number to fetch for FETCH_RELATIVE SPI_processed and SPI_tuptable are set as in SPI_execute if successful. See the SQL command for details of the interpretation of the direction and count parameters. Direction values other than FETCH_FORWARD may fail if the cursor's plan was not created with the CURSOR_OPT_SCROLL option. SPI_scroll_cursor_move 3 SPI_scroll_cursor_move move a cursor SPI_scroll_cursor_move void SPI_scroll_cursor_move(Portal portal, FetchDirection direction, long count) SPI_scroll_cursor_move skips over some number of rows in a cursor. This is equivalent to the SQL command MOVE. Portal portal portal containing the cursor FetchDirection direction one of FETCH_FORWARD, FETCH_BACKWARD, FETCH_ABSOLUTE or FETCH_RELATIVE long count number of rows to move for FETCH_FORWARD or FETCH_BACKWARD; absolute row number to move to for FETCH_ABSOLUTE; or relative row number to move to for FETCH_RELATIVE SPI_processed is set as in SPI_execute if successful. SPI_tuptable is set to NULL, since no rows are returned by this function. See the SQL command for details of the interpretation of the direction and count parameters. Direction values other than FETCH_FORWARD may fail if the cursor's plan was not created with the CURSOR_OPT_SCROLL option. SPI_cursor_close 3 SPI_cursor_close close a cursor SPI_cursor_close void SPI_cursor_close(Portal portal) SPI_cursor_close closes a previously created cursor and releases its portal storage. All open cursors are closed automatically at the end of a transaction. SPI_cursor_close need only be invoked if it is desirable to release resources sooner. Portal portal portal containing the cursor SPI_saveplan 3 SPI_saveplan save a plan SPI_saveplan SPIPlanPtr SPI_saveplan(SPIPlanPtr plan) SPI_saveplan saves a passed plan (prepared by SPI_prepare) in memory that will not be freed by 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. SPIPlanPtr plan the plan to be saved Pointer to the saved plan; NULL if unsuccessful. On error, SPI_result is set thus: SPI_ERROR_ARGUMENT if plan is NULL or invalid SPI_ERROR_UNCONNECTED 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 until SPI_finish. 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. The functions described here provide an interface for extracting information from result sets returned by SPI_execute and other SPI functions. All functions described in this section can be used by both connected and unconnected procedures. SPI_fname 3 SPI_fname determine the column name for the specified column number SPI_fname char * SPI_fname(TupleDesc rowdesc, int colnumber) SPI_fname returns a copy of the column name of the specified column. (You can use pfree to release the copy of the name when you don't need it anymore.) TupleDesc rowdesc input row description int colnumber column number (count starts at 1) The column name; NULL if colnumber is out of range. SPI_result set to SPI_ERROR_NOATTRIBUTE on error. SPI_fnumber 3 SPI_fnumber determine the column number for the specified column name SPI_fnumber int SPI_fnumber(TupleDesc rowdesc, const char * colname) SPI_fnumber returns the column number for the column with the specified name. If colname refers to a system column (e.g., oid) then the appropriate negative column number will be returned. The caller should be careful to test the return value for exact equality to SPI_ERROR_NOATTRIBUTE to detect an error; testing the result for less than or equal to 0 is not correct unless system columns should be rejected. TupleDesc rowdesc input row description const char * colname column name Column number (count starts at 1), or SPI_ERROR_NOATTRIBUTE if the named column was not found. SPI_getvalue 3 SPI_getvalue return the string value of the specified column SPI_getvalue char * SPI_getvalue(HeapTuple row, TupleDesc rowdesc, int colnumber) SPI_getvalue returns the string representation of the value of the specified column. The result is returned in memory allocated using palloc. (You can use pfree to release the memory when you don't need it anymore.) HeapTuple row input row to be examined TupleDesc rowdesc input row description int colnumber column number (count starts at 1) Column value, or NULL if the column is null, colnumber is out of range (SPI_result is set to SPI_ERROR_NOATTRIBUTE), or no output function is available (SPI_result is set to SPI_ERROR_NOOUTFUNC). SPI_getbinval 3 SPI_getbinval return the binary value of the specified column SPI_getbinval Datum SPI_getbinval(HeapTuple row, TupleDesc rowdesc, int colnumber, bool * isnull) SPI_getbinval returns the value of the specified column in the internal form (as type Datum). This function does not allocate new space for the datum. In the case of a pass-by-reference data type, the return value will be a pointer into the passed row. HeapTuple row input row to be examined TupleDesc rowdesc input row description int colnumber column number (count starts at 1) bool * isnull flag for a null value in the column The binary value of the column is returned. The variable pointed to by isnull is set to true if the column is null, else to false. SPI_result is set to SPI_ERROR_NOATTRIBUTE on error. SPI_gettype 3 SPI_gettype return the data type name of the specified column SPI_gettype char * SPI_gettype(TupleDesc rowdesc, int colnumber) SPI_gettype returns a copy of the data type name of the specified column. (You can use pfree to release the copy of the name when you don't need it anymore.) TupleDesc rowdesc input row description int colnumber column number (count starts at 1) The data type name of the specified column, or NULL on error. SPI_result is set to SPI_ERROR_NOATTRIBUTE on error. SPI_gettypeid 3 SPI_gettypeid return the data type OID of the specified column SPI_gettypeid Oid SPI_gettypeid(TupleDesc rowdesc, int colnumber) SPI_gettypeid returns the OID of the data type of the specified column. TupleDesc rowdesc input row description int colnumber column number (count starts at 1) The OID of the data type of the specified column or InvalidOid on error. On error, SPI_result is set to SPI_ERROR_NOATTRIBUTE. SPI_getrelname 3 SPI_getrelname return the name of the specified relation SPI_getrelname char * SPI_getrelname(Relation rel) SPI_getrelname returns a copy of the name of the specified relation. (You can use pfree to release the copy of the name when you don't need it anymore.) Relation rel input relation The name of the specified relation. SPI_getnspname 3 SPI_getnspname return the namespace of the specified relation SPI_getnspname char * SPI_getnspname(Relation rel) SPI_getnspname returns a copy of the name of the namespace that the specified Relation belongs to. This is equivalent to the relation's schema. You should pfree the return value of this function when you are finished with it. Relation rel input relation The name of the specified relation's namespace. PostgreSQL allocates memory within memory contextsmemory contextin SPI, which provide a convenient method of managing allocations made in many different places that need to live for differing amounts of time. Destroying a context releases all the memory that was allocated in it. Thus, it is not necessary to keep track of individual objects to avoid memory leaks; instead only a relatively small number of contexts have to be managed. palloc and related functions allocate memory from the current context. SPI_connect creates a new memory context and makes it current. SPI_finish restores the previous current memory context and destroys the context created by SPI_connect. These actions ensure that transient memory allocations made inside your procedure are reclaimed at procedure exit, avoiding memory leakage. However, if your procedure needs to return an object in allocated memory (such as a value of a pass-by-reference data type), you cannot allocate that memory using palloc, at least not while you are connected to SPI. If you try, the object will be deallocated by SPI_finish, and your procedure will not work reliably. To solve this problem, use SPI_palloc to allocate memory for your return object. SPI_palloc allocates memory in the upper executor context, that is, the memory context that was current when SPI_connect was called, which is precisely the right context for a value returned from your procedure. If SPI_palloc is called while the procedure is not connected to SPI, then it acts the same as a normal palloc. Before a procedure connects to the SPI manager, the current memory context is the upper executor context, so all allocations made by the procedure via palloc or by SPI utility functions are made in this context. When SPI_connect is called, the private context of the procedure, which is created by SPI_connect, is made the current context. All allocations made by palloc, repalloc, or SPI utility functions (except for SPI_copytuple, SPI_returntuple, SPI_modifytuple, and SPI_palloc) are made in this context. When a procedure disconnects from the SPI manager (via SPI_finish) the current context is restored to the upper executor context, and all allocations made in the procedure memory context are freed and cannot be used any more. All functions described in this section can be used by both connected and unconnected procedures. In an unconnected procedure, they act the same as the underlying ordinary server functions (palloc, etc.). SPI_palloc 3 SPI_palloc allocate memory in the upper executor context SPI_palloc void * SPI_palloc(Size size) SPI_palloc allocates memory in the upper executor context. Size size size in bytes of storage to allocate pointer to new storage space of the specified size SPI_repalloc 3 SPI_repalloc reallocate memory in the upper executor context SPI_repalloc void * SPI_repalloc(void * pointer, Size size) SPI_repalloc changes the size of a memory segment previously allocated using SPI_palloc. This function is no longer different from plain repalloc. It's kept just for backward compatibility of existing code. void * pointer pointer to existing storage to change Size size size in bytes of storage to allocate pointer to new storage space of specified size with the contents copied from the existing area SPI_pfree 3 SPI_pfree free memory in the upper executor context SPI_pfree void SPI_pfree(void * pointer) SPI_pfree frees memory previously allocated using SPI_palloc or SPI_repalloc. This function is no longer different from plain pfree. It's kept just for backward compatibility of existing code. void * pointer pointer to existing storage to free SPI_copytuple 3 SPI_copytuple make a copy of a row in the upper executor context SPI_copytuple HeapTuple SPI_copytuple(HeapTuple row) SPI_copytuple makes a copy of a row in the upper executor context. This is normally used to return a modified row from a trigger. In a function declared to return a composite type, use SPI_returntuple instead. HeapTuple row row to be copied the copied row; NULL only if tuple is NULL SPI_returntuple 3 SPI_returntuple prepare to return a tuple as a Datum SPI_returntuple HeapTupleHeader SPI_returntuple(HeapTuple row, TupleDesc rowdesc) SPI_returntuple makes a copy of a row in the upper executor context, returning it in the form of a row type Datum. The returned pointer need only be converted to Datum via PointerGetDatum before returning. Note that this should be used for functions that are declared to return composite types. It is not used for triggers; use SPI_copytuple for returning a modified row in a trigger. HeapTuple row row to be copied TupleDesc rowdesc descriptor for row (pass the same descriptor each time for most effective caching) HeapTupleHeader pointing to copied row; NULL only if row or rowdesc is NULL SPI_modifytuple 3 SPI_modifytuple create a row by replacing selected fields of a given row SPI_modifytuple HeapTuple SPI_modifytuple(Relation rel, HeapTuple row, int ncols, int * colnum, Datum * values, const char * nulls) SPI_modifytuple creates a new row by substituting new values for selected columns, copying the original row's columns at other positions. The input row is not modified. Relation rel Used only as the source of the row descriptor for the row. (Passing a relation rather than a row descriptor is a misfeature.) HeapTuple row row to be modified int ncols number of column numbers in the array colnum int * colnum array of the numbers of the columns that are to be changed (column numbers start at 1) Datum * values new values for the specified columns const char * Nulls which new values are null, if any (see SPI_execute_plan for the format) new row with modifications, allocated in the upper executor context; NULL only if row is NULL On error, SPI_result is set as follows: SPI_ERROR_ARGUMENT if rel is NULL, or if row is NULL, or if ncols is less than or equal to 0, or if colnum is NULL, or if values is NULL. SPI_ERROR_NOATTRIBUTE if colnum contains an invalid column number (less than or equal to 0 or greater than the number of column in row) SPI_freetuple 3 SPI_freetuple free a row allocated in the upper executor context SPI_freetuple void SPI_freetuple(HeapTuple row) SPI_freetuple frees a row previously allocated in the upper executor context. This function is no longer different from plain heap_freetuple. It's kept just for backward compatibility of existing code. HeapTuple row row to free SPI_freetuptable 3 SPI_freetuptable free a row set created by SPI_execute or a similar function SPI_freetuptable void SPI_freetuptable(SPITupleTable * tuptable) SPI_freetuptable frees a row set created by a prior SPI command execution function, such as SPI_execute. Therefore, this function is usually called with the global variable SPI_tupletable 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. SPITupleTable * tuptable pointer to row set to free SPI_freeplan 3 SPI_freeplan free a previously saved plan SPI_freeplan int SPI_freeplan(SPIPlanPtr plan) SPI_freeplan releases a command execution plan previously returned by SPI_prepare or saved by SPI_saveplan. SPIPlanPtr plan pointer to plan to free SPI_ERROR_ARGUMENT if plan is NULL or invalid The following rules govern the visibility of data changes in functions that use SPI (or any other C function): During the execution of an SQL command, any data changes made by the command are invisible to the command itself. For example, in: INSERT INTO a SELECT * FROM a; the inserted rows are invisible to the SELECT part. Changes made by a command C are visible to all commands that are started after C, no matter whether they are started inside C (during the execution of C) or after C is done. Commands executed via SPI inside a function called by an SQL command (either an ordinary function or a trigger) follow one or the other of the above rules depending on the read/write flag passed to SPI. Commands executed in read-only mode follow the first rule: they cannot see changes of the calling command. Commands executed in read-write mode follow the second rule: they can see all changes made so far. All standard procedural languages set the SPI read-write mode depending on the volatility attribute of the function. Commands of STABLE and IMMUTABLE functions are done in read-only mode, while commands of VOLATILE functions are done in read-write mode. While authors of C functions are able to violate this convention, it's unlikely to be a good idea to do so. The next section contains an example that illustrates the application of these rules. This section contains a very simple example of SPI usage. The procedure execq takes an SQL command as its first argument and a row count as its second, executes the command using SPI_exec and returns the number of rows that were processed by the command. You can find more complex examples for SPI in the source tree in src/test/regress/regress.c and in contrib/spi. #include "postgres.h" #include "executor/spi.h" #include "utils/builtins.h" #ifdef PG_MODULE_MAGIC PG_MODULE_MAGIC; #endif int execq(text *sql, int cnt); int execq(text *sql, int cnt) { char *command; int ret; int proc; /* Convert given text object to a C string */ command = text_to_cstring(sql); SPI_connect(); ret = SPI_exec(command, cnt); proc = SPI_processed; /* * If some rows were fetched, print them via elog(INFO). */ if (ret > 0 && SPI_tuptable != NULL) { TupleDesc tupdesc = SPI_tuptable->tupdesc; SPITupleTable *tuptable = SPI_tuptable; char buf[8192]; int i, j; for (j = 0; j < proc; j++) { HeapTuple tuple = tuptable->vals[j]; for (i = 1, buf[0] = 0; i <= tupdesc->natts; i++) snprintf(buf + strlen (buf), sizeof(buf) - strlen(buf), " %s%s", SPI_getvalue(tuple, tupdesc, i), (i == tupdesc->natts) ? " " : " |"); elog(INFO, "EXECQ: %s", buf); } } SPI_finish(); pfree(command); return (proc); } (This function uses call convention version 0, to make the example easier to understand. In real applications you should use the new version 1 interface.) This is how you declare the function after having compiled it into a shared library (details are in .): CREATE FUNCTION execq(text, integer) RETURNS integer AS 'filename' LANGUAGE C; Here is a sample session: => SELECT execq('CREATE TABLE a (x integer)', 0); execq ------- 0 (1 row) => INSERT INTO a VALUES (execq('INSERT INTO a VALUES (0)', 0)); INSERT 0 1 => SELECT execq('SELECT * FROM a', 0); INFO: EXECQ: 0 -- inserted by execq INFO: EXECQ: 1 -- returned by execq and inserted by upper INSERT execq ------- 2 (1 row) => SELECT execq('INSERT INTO a SELECT x + 2 FROM a', 1); execq ------- 1 (1 row) => SELECT execq('SELECT * FROM a', 10); INFO: EXECQ: 0 INFO: EXECQ: 1 INFO: EXECQ: 2 -- 0 + 2, only one row inserted - as specified execq ------- 3 -- 10 is the max value only, 3 is the real number of rows (1 row) => DELETE FROM a; DELETE 3 => INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1); INSERT 0 1 => SELECT * FROM a; x --- 1 -- no rows in a (0) + 1 (1 row) => INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1); INFO: EXECQ: 1 INSERT 0 1 => SELECT * FROM a; x --- 1 2 -- there was one row in a + 1 (2 rows) -- This demonstrates the data changes visibility rule: => INSERT INTO a SELECT execq('SELECT * FROM a', 0) * x FROM a; INFO: EXECQ: 1 INFO: EXECQ: 2 INFO: EXECQ: 1 INFO: EXECQ: 2 INFO: EXECQ: 2 INSERT 0 2 => SELECT * FROM a; x --- 1 2 2 -- 2 rows * 1 (x in first row) 6 -- 3 rows (2 + 1 just inserted) * 2 (x in second row) (4 rows) ^^^^^^ rows visible to execq() in different invocations