[FLINK-21935] Remove "state.backend.async" option.

• Type: Improvement
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Fix Version/s: 1.13.0
• Component/s: Runtime / State Backends
• Labels: pull-request-available

Release Note

The 'state.backend.async' option is deprecated.
Snapshots are always asynchronous now (as they were by default before) and there is no option to configure a synchronous snapshot any more.

The constructors of "FsStateBackend" and "MemoryStateBackend" that take a flag for sync/async snapshots are kept for API compatibility, but the flags are ignored now.

• Assignee: Stephan Ewen
• Reporter: Stephan Ewen
• Created: 23/Mar/21 18:56
• Updated: 07/Oct/21 13:41
• Resolved: 01/Apr/21 16:03

Description

Checkpoints are always asynchronous, there is no case ever for a synchronous checkpoint.
The RocksDB state backend doesn't even support synchronous snapshots, and the HashMap Heap backend also has no good use case for synchronous snapshots (other than a very minor reduction in heap objects).

Most importantly, we should not expose this option in the constructors of the new state backend API classes, like HashMapStateBackend.

I marked this a blocker because it is part of the new user-facing State Backend API and I would like to avoid that this option enters this API and causes confusion when we eventually remove it.

/cc Seth Wiesman and Yu Li

Issue Links

• causes: FLINK-22444 Drop async checkpoint description of state backends in Chinese docs
• is related to: FLINK-22187 Remove description of sync checkpoint mode of HashMapStateBackend
• relates to: FLINK-24475 Remove no longer used NestedMap* classes
• links to: GitHub Pull Request #15429