[FLINK-30554][sql-client] Remove useless sessionId in the Executor

[fsk119]

What is the purpose of the change

Remove useless sessionId in the Executor. The SQL Gateway uses the SessionHandle to identify each Session and the SessionHandle is assigned by the Gateway only. The Executor in the SqlClient is the client to submit messages to the
Gateway and it is only used by the current Session. We don't need to use the sessionId everywhere.

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): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• 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)

[flinkbot]

CI report:

• 23fba07 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

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

[fsk119]

@flinkbot run azure

[swuferhong]

Thanks for the contribution @fsk119 , I left some comments

[swuferhong]

I have one question. Original LocalExecutor implements Executor have a map ConcurrentHashMap<String, SessionContext> contextMap, but now, we just delete it. Does this mean that each executor can only have one session? (If that, why we need sessionId, we can just define an executorId instead ? ). Also, I think if you delete this contextMap, you need add tests to verify we don't need this map. WDYT ？

[fsk119]

Does this mean that each executor can only have one session?

Yes, you are right. Executor only works for one session in the new design. The Gateway is designed for the multitenancy.

why we need sessionId, we can just define an executorId instead?

I think session id is still useful. For example, SQL Client can convey the user name/password with the current API. So I am prone to keep it unchanged and prepare for the future authentication mechanism.

[swuferhong]

Ok, I got it.

[fsk119]

@flinkbot run azure

[swuferhong]

LGTM +1