StephanEwen opened a new pull request #6726: [FLINK-9061] [s3] Add entropy injection to S3 file systems for checkpoints URL: https://github.com/apache/flink/pull/6726 ## What is the purpose of the change This pull request adds hooks to optionally inject entropy to the checkpoint path based upon a user defined pattern in the configuration for better S3 scalability. This is a revised version of #6302 by @indrc (based on Flink 1.4) that ports the changes to the new FileStateStorage code introduced in Flink 1.5 and to the new S3 common abstraction recently added to the master branch. The difference to the previous approach is that the entropy injection sits only in the S3 file system code and the checkpointing code only passes a write option that says that entropy is desired here. The advantage of that is that the checkpointing code stays simple. Furthermore, entropy injection is only configurable for S3, which is the only FS that can support this style of path rewriting properly, because it is actually an object store and can handle random injection in the paths without causing "parent does not exist" directory problems. ## Brief change log - Extends the FileSystem class with a `write(Path, WriteOptions)` method. This method should subsume all special methods with extra options that are relevant to a subset of file systems. The `WriteOptions` object makes this extensible without breaking the API. - Adds an implementation of entropy injection for the base S3 file system from which the Presto-based and Hadoop-based S3 file systems inherit. When entropy injection is configured and requested, the entropy key is replaced in the path, otherwise filtered out. - The only change in checkpointing is that the `FsCheckpointStreamFactory` passes the specific WriteOption to "inject entropy here if configured". ## Verifying this change - Added unit test for entropy injection under `org.apache.flink.runtime.state.filesystem` - Added unit test for checkpointing under `org.apache.flink.fs.s3.common` ## 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, Yarn/Mesos, ZooKeeper: **no** - The S3 file system connector: **yes** ## Documentation - Does this pull request introduce a new feature? **yes** - If yes, how is the feature documented? **docs**
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