[FLINK-25960][network] Distribute the data read buffers more fairly among result partitions for sort-shuffle

[wsry]

What is the purpose of the change

Currently, the data read buffers for sort-shuffle are allocated in a random way and some result partitions may occupy too many buffers which leads to the starvation of other result partitions. This patch improves the scenario by not reading data for those result partitions which already occupy more than the average number of read buffers per result partition.

Brief change log

• Not reading data for those result partitions which already occupy more than the average number of read buffers per result partition.

Verifying this change

This change is already covered by existing tests.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
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• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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CI report:

• 5f419a2 Azure: SUCCESS

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Last check on commit c1b720b (Fri Feb 04 13:01:49 UTC 2022)

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[gaoyunhaii]

Thanks @wsry for the PR! LGTM