[FLINK-37382][runtime] Early optimization for adaptive join when either input is below broadcast threshold.

[SinBex]

What is the purpose of the change

When the large table side has not yet initialized, if the small table side finishes early and the output data volume is smaller than the broadcast threshold, the adaptive join operator can be optimized to a broadcast hash join in advance. This can help reduce network shuffle overhead.

Brief change log

• The adaptive broadcast join optimization is triggered in advance when any input of the join node meets the broadcast condition.

Verifying this change

This change is already covered by existing tests, such as (please describe tests).

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, ZooKeeper: (no)
• The S3 file system connector: (no )

Documentation

• Does this pull request introduce a new feature? (no)

[flinkbot]

CI report:

• e114ebb Azure: FAILURE
• 6230060 Azure: PENDING

Bot commands

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• @flinkbot run azure re-run the last Azure build

[JunRuiLee]

Thanks @SinBex for fix, most of it looks good. I left two minor comments, PTAL~

[SinBex]

Thanks to @JunRuiLee for reviewing, all comments have been fixed, PTAL

[JunRuiLee]

Thanks @SinBex , LGTM.

[JunRuiLee]

This GHA shows that the flink-connect tests have passed, which reverted FLINK-36585. You can find more details at https://github.com/SinBex/flink/actions/runs/13537602087.