[FLINK-23473][runtime] Do not create transaction in TwoPhaseCommitSinkFunction after finish

[curcur]

What is the purpose of the change

Do not create transactions in TwoPhaseCommitSinkFunction after finish() is called. The reason is that after finish() is called, no more input is expected and hence no more transactions are needed.

The problem of creating transactions is that there would be one/or possibly several open transactions that would be never closed after the task finishes.

Brief change log

Introduce empty transaction holder; so that after sink function is closed, we will place empty transaction as a holder.

Verifying this change

• add unit tests
• existing unit tests + ITTests.

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: (affect recovery that uses two-phase commit, like Kafka)
• The S3 file system connector: (no)

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Last check on commit aa88f9f (Tue Aug 10 13:01:18 UTC 2021)

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[akalash]

@curcur , the changes LGTM but I don't sure that one test covers all these changes. I will think about test cases yet but if you think that it is enough please share your opinion.

[akalash]

LGTM

[curcur]

rebase.

[curcur]

Thanks for reviewing @akalash

[curcur]

build -> green:

https://dev.azure.com/apache-flink/apache-flink/_build/results?buildId=22087&view=results