StephanEwen opened a new pull request #11202: [FLINK-16247][checkpoints] Various cleanups in checkpointing code URL: https://github.com/apache/flink/pull/11202 ## Prerequisite *This PR is based on #11179* ## What is the purpose of the change **This is part of the preparation for implementing Fault Tolerance for Operator Coordinators for the new Source Interface (FLIP-27).** The PR contains various cleanups and simplifications to the checkpoint metadata handling code. ## Brief change log - [FLINK-16247][checkpoints] Rename 'checkpoints.savepoint.' package and classes to 'checkpoint.metadata.' These classes describe the persistence of checkpoint metadata. Originally, savepoints where the only snapshots with persistent metadata, while checkpoints had the metadata only in memory or in ZooKeeper (Java Serialized). Nowadays, checkpoints and savepoints both persist metadata in the same way, and hence the package is not actually related to savepoints any more. - [FLINK-16259][checkpoints] Drop interface/impl separation for checkpoint Metadata and rename MetadataV2 to CheckpointMetadata The interface 'Metadata' (nee Savepoint) and its different implementations was misleading. There is only ever one real implementation: the latest version. All deserializers need to go to that version, to keep the complex versioning logic out of other parts of the code. Further more, this is a simple "data holder" class, simply storing collections, there is no behavior to be abstracted behind an interface. Even if there were different versions (as in an earlier version of the code, where the SavepointV1 class for tests was in the main scope), the interface was a union of all accessors to all different collections from different versions (with all accessors but the ones for the latest version deprecated). As a result, the 'Metadata' interface was misleading and suggesting something that is not there, namely that multiple versions of the metadata are handled in various places in the code, and not just during deserialization. ## Verifying this change This change is pure refactoring without any changes to functionality. ## Does this pull request potentially affect one of the following parts: - Dependencies (does it add or upgrade a dependency): **no** - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: **no** - The serializers: **no** - The runtime per-record code paths (performance sensitive): **no** - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: **no** - The S3 file system connector: **no** ## Documentation - Does this pull request introduce a new feature? **no** - If yes, how is the feature documented? **not applicable**
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