[FLINK-12121] Use composition instead of inheritance for the InternalKeyContext logic in backend

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.9.0
• Component/s: Runtime / State Backends
• Labels: pull-request-available
• Assignee: Yu Li
• Reporter: Yu Li
• Created: 08/Apr/19 08:51
• Updated: 10/Apr/19 08:00
• Resolved: 10/Apr/19 08:00

Description

Commonly it's recommended to favor composition over inheritance in java design, but currently in keyed backend we're using inheritance for the InternalKeyContext logic, and here we propose to change to the composition way.

Another advantage of changing to the composition way is that we could remove the requirement of a heap backend instance when constructing HeapRestoreOperation, and further making sure all fields are final when constructing the HeapKeyedStateBackend

Issue Links

• blocks: FLINK-12066 Remove StateSerializerProvider field in keyed state backend
• links to: GitHub Pull Request #8122