[IMPALA-4711] Document is_null semantics in UDF interface

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 2.7.0
• Fix Version/s: Impala 2.9.0
• Component/s: Backend
• Labels: documentation usability
• Target Version: Product Backlog
• Assignee: Tim Armstrong
• Reporter: Tim Armstrong
• Created: 23/Dec/16 14:42
• Updated: 08/Mar/17 06:19
• Resolved: 08/Mar/17 06:19

Description

A user ran into some confusion about the semantics of the is_null field of *Val classes in the UDF interface. The intended semantics are that if is_null is true, then no other fields in the class are valid. E.g. StringVal::len and StringVal::ptr.

However, this isn't explicitly documented anywhere and a user assumed that is_null == true implies that the other fields should be initialised to len == 0 and ptr == NULL