[FLINK-17865][checkpoint] Increase default size of 'state.backend.fs.memory-threshold'

[Myasuka]

What is the purpose of the change

Increase the default value of state.backend.fs.memory-threshold from 1K to 20K as thread discussed.

Brief change log

Increase default size of 'state.backend.fs.memory-threshold' from 1k to 20k

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

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: yes
• 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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Automated Checks

Last check on commit 5771a99 (Thu May 28 06:39:42 UTC 2020)

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• ❓ 1. The [description] looks good.
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• ❓ 5. Overall code [quality] is good.

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CI report:

• 5771a99 Azure: SUCCESS

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[carp84]

+1, thanks for the efforts @Myasuka