[FLINK-2676] Add abstraction for keyed window state

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 0.10.0
• Fix Version/s: 1.0.0
• Component/s: API / DataStream
• Assignee: Stephan Ewen
• Reporter: Stephan Ewen
• Created: 15/Sep/15 12:13
• Updated: 28/Feb/19 11:15
• Resolved: 17/Nov/15 13:22

Description

This abstraction should help to seamlessly switch between window state kept as

• Heap-resident maps
• Managed memory spillable maps
• key/value state backend state

I would approach this abstraction once we implemented a few window operators and see what operations we need, such as

• Drop time-regions across all keys
• Append to state for key
• Update/replace state by key
• Iterate over unions of multiple state time regions
• snapshot time regions completely / incrementally
• (possibly more)