Obtain a function descriptor
A function descriptor, MI_FUNC_DESC, contains static information about a UDR that is to be invoked with the Fastpath interface. It is basically a structured version of the row in the sysprocedures system catalog table that describes the UDR. The function descriptor also identifies the routine sequence for the associated UDR.
The following table summarizes the memory operations for
a function descriptor.
| Memory duration | Memory operation | Function name |
|---|---|---|
| PER_COMMAND | Constructor | mi_cast_get(), mi_func_desc_by_typeid(), mi_routine_get(), mi_routine_get_by_typeid(), mi_td_cast_get() |
| PER_COMMAND | Destructor | mi_routine_end() |
Tip: Function descriptors are stored with the
connection descriptor. Because a connection descriptor has a PER_COMMAND
duration, so too does a function descriptor. However, it is possible
to obtain a session-duration connection descriptor and, consequently,
session-duration function descriptors.
A calling DataBlade®
API module
uses a function descriptor as a handle to identify the UDR it needs
to invoke with the Fastpath interface. To obtain a function descriptor,
call one of the Fastpath look-up functions in the following table.
| Type of UDRs | Fastpath look-up function |
|---|---|
| Looking up general UDRs | mi_func_desc_by_typeid(), mi_routine_get(), mi_routine_get_by_typeid() |
| Looking up cast functions | mi_cast_get(), mi_td_cast_get() |