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.

Table 1. Non-PDQ-threadsafe DataBlade API functions
Table showing the non-PDQ-threadsafe DataBlade API functions, category, and task. The rows list the category, followed by the task.
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 Input-parameter information in the statement descriptor)
	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 Save-set functions of the DataBlade API)
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 Data type information in a type descriptor ) Column functions if they access a complex type: mi_column_* (see Field and column information in the row descriptor)
Operating-system file access		All file-access functions: mi_file_* (see DataBlade API file-access functions )
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 Non-PDQ-threadsafe DataBlade API functions. 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 Non-PDQ-threadsafe DataBlade API functions, it cannot be parallelizable.

Keep in mind the following considerations when you write a UDR to 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).