Purpose
Designates a table function as the controlling copy of all other copies of the table function running on other AMP vprocs.
Syntax
int FNC_TblControl(void)
Return Value
| IF the call is … | THEN FNC_TblControl returns … |
|---|---|
| successful and the copy of table function can take the control role of the table function | 1. |
| not successful and the copy of the table function should not assume the role of the control copy | 0. |
Valid Invocation Mode
Use this library function when the return value of FNC_GetPhase is TBL_MODE_CONST, indicating that the SELECT statement invoked the table function with constant expression input arguments.
For example:
SELECT *
FROM TABLE (table_function_1('STRING_CONSTANT'))
AS table_1;
Usage Notes
Setting up a controlling copy of a table function is useful when there is a need to distribute certain external control data among various copies of the table function that run on different AMP vprocs, but the external control data is on a particular node that only one copy of the table function can access.
Only one copy of the table function can successfully call FNC_TblControl.
After calling FNC_TblControl, the controlling copy of a table function can distribute control data to other table function copies by calling FNC_TblAllocCtrlCtx to allocate a control scratchpad.
Restrictions
This function can only be called from within a table function. Calling this function from a scalar function, aggregate function, UDM, or external stored procedure results in an exception on the transaction.
This function can only be called once.
A table function that calls FNC_TblControl cannot also call FNC_TblFirstParticipant.
- TBL_MODE_CONST for the FNC_Mode result
- TBL_PRE_INIT for the FNC_Phase output argument
Example Using FNC_TblControl
typedef struct {
unsigned short cntrl_fnc_AMP
int qfd;
...
} ctrl_ctx;
ctrl_ctx *options;
AMP_Info_t *LocalConfig;
FNC_Phase Phase;
if (FNC_GetPhase(&Phase) == TBL_MODE_CONST)
{
switch(Phase)
{
case TBL_PRE_INIT:
{
LocalConfig = FNC_AMPInfo();
if ( FNC_TblControl() ) {
options = FNC_TblAllocCtrlCtx(sizeof(ctrl_ctx));
options->ctrl_fnc_AMP = LocalConfig->AMPId;
...
}
}
...
}
}
...