Write the parallelizable UDR
To write a parallelizable C UDR, you must ensure that the UDR does not include any calls to the non-PDQ-threadsafe DataBlade API functions.
The following table lists non-PDQ-threadsafe DataBlade API functions.
| Category of non-PDQ-threadsafe function | DataBlade API function | |
|---|---|---|
| Statement processing: | ||
| Statement execution A parallelizable UDR cannot parse an SQL statement. |
mi_exec(), mi_prepare() | |
| Current-statement processing No current statement exists in a parallelizable UDR. Therefore, these functions are not useful. |
mi_binary_query(), mi_command_is_finished(), mi_get_result(), mi_get_row_desc_without_row(), mi_next_row(), mi_query_finish(), mi_query_interrupt(), mi_result_command_name(), mi_result_row_count(), mi_value(), mi_value_by_name() | |
| Prepared statements No prepared statement exists because you cannot prepare one in a parallelizable UDR. Therefore, these functions are not useful. |
mi_close_statement(), mi_drop_prepared_statement(), mi_exec_prepared_statement(), mi_fetch_statement(), mi_get_statement_row_desc(), mi_open_prepared_statement(), mi_statement_command_name()
All input-parameter accessor functions: mi_parameter_* (see Table 1) |
|
| Transfer of data Even though these type-transfer functions are PDQ-threadsafe, they are usually called within the send and receive support functions of an opaque type and are likely to be called during statement processing. |
All type-transfer functions: mi_get_*, mi_put_* (see Conversion of opaque-type data with computer-specific data types) | |
| Other | mi_current_command_name() | |
| Save-set handling | All save-set functions: mi_save_set_* (see Table 1) | |
| Complex-type (collections and row types) handling: | ||
| Collection processing | All collection functions: mi_collection_* (see Collections) | |
| Row-type processing | mi_get_row_desc(), mi_get_row_desc_from_type_desc(), mi_get_row_desc_without_row(), mi_get_statement_row_desc()
mi_row_create(), mi_row_free(), mi_row_desc_create(), mi_row_desc_free() |
|
| Complex-type processing | Type-descriptor accessor functions if they access
a complex type: mi_type_* (see Table 1) Column functions if they access a complex type: mi_column_* (see Table 1) |
|
| Operating-system file access | All file-access functions: mi_file_* (see Table 1) | |
| Tracing: | ||
| Even though the files listed here are not PDQ-threadsafe, you can include most statements that generate trace output in a parallelizable UDR. | mi_tracefile_set(), mi_tracelevel_set() GL_DPRINTF | |
| Miscellaneous | mi_get_connection_option(), mi_get_database_info(), mi_get_session_connection(), mi_get_type_source_type() | |
A parallelizable C UDR cannot call (either explicitly or implicitly) any of the DataBlade API functions in Table 1. If you attempt to run a UDR that contains a non-PDQ-threadsafe function in parallel, the database server generates an error. If your UDR must call one of the functions in Table 1, it cannot be parallelizable.
- For a UDR that operates on an opaque type to be parallelizable, all support functions of the opaque type must be parallelizable.
- A UDR that operates on complex data types cannot be parallelizable.
- A UDR can be parallelizable whether it runs in the CPU VP or a user-defined VP.
- A UDR that acts as a functional index cannot be parallelizable.
- A UDR that is parallelizable cannot call a UDR that is not parallelizable (either explicitly or with the Fastpath interface).