RainerMatthiasS opened a new pull request, #23239:
URL: https://github.com/apache/flink/pull/23239
## Contribution Checklist
- `Pending:` Make sure that the change passes the automated tests, i.e.,
`mvn clean verify` passes. You can set up Azure Pipelines CI to do that
following [this
guide](https://cwiki.apache.org/confluence/display/FLINK/Azure+Pipelines#AzurePipelines-Tutorial:SettingupAzurePipelinesforaforkoftheFlinkrepository).
## What is the purpose of the change
Avoids a known flaw in Stream.flatMap, see
https://bugs.openjdk.org/browse/JDK-8267359. Avoids potential OOM Error for
keyed state with many keys when reading them with state processor api.
## Brief change log
- replaced the original implementation of MultiStateKeyIterator with a
Java-Stream-free implementation.
- this fixes a known flaw in Stream.flatMap which leads to complete
enumeration of inner iterator
and buffering of all elements with potential for a OOM error for state
with many keys
- manual implementation of nested iterator avoids this problem
## Verifying this change
This change adds a tests
MultiStateKeyIteratorTest#testIteratorPullsSingleKeyFromAllDescriptors that
fails with the previous implementation and succeeds with the new implementation.
## 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
- new code should be marginally faster (not verified)
- Anything that affects deployment or recovery: JobManager (and its
components), Checkpointing, Kubernetes/Yarn, 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? JavaDocs
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