[BEAM-2902] Add user state support for ParDo.Multi for the Dataflow runner

• Type: Sub-task
• Status: Resolved
• Priority: P3
• Resolution: Fixed
• Fix Version/s: 2.21.0
• Component/s: runner-dataflow
• Labels: portability sickbay
• Assignee: Luke Cwik
• Reporter: Luke Cwik
• Created: 11/Sep/17 20:07
• Updated: 16/May/20 13:25
• Resolved: 15/May/20 18:36

Description

Add support for user state in a ParDo.Multi by:

• adding expansion/conversion logic within Dataflow service to add any needed GBKs to allow expansion.

OR

• Add support for expansion inside the Beam SDK once the PTransformMatcher exposes a way to know when the replacement is not required by checking that the preceding ParDos to a GBK are key preserving.