The external_UDF_execution_mode option controls the amount of error checking and call tracing that is performed when statements involving v3 and v4 external user-defined functions are evaluated.
You can use external_UDF_execution_mode during development of a UDF to aid in debugging while you are developing UDFs.
When set to 0, the default, external UDFs are evaluated in a manner that optimizes the performance of statements using UDFs.
When set to 1, external UDFs are evaluated to validate the information passed back and forth to each UDF. This setting is intended for scalar and aggregate UDFs.
When set to 2, external UDFs are evaluated to not only validate the information passed back and forth to the UDF, but also to log, in the iqmsg file, every call to the functions provided by the UDFs and every callback from those functions back into the server. This setting is intended for all C or C++ external UDFs. Memory tracing is turned on for table UDFs and TPFs.