Add support for closing a database (session)

[kou]

It seems that Apache Arrow Flight SQL doesn't provide a command that closes the current session explicitly: https://arrow.apache.org/docs/format/FlightSql.html

In https://lists.apache.org/thread/0w25o85y8vsndz87kpjljxz24x077o3y , using a custom (close) action was suggested.

@lidavidm Is using a custom close action still a suggested approach to close the current session? I have a concern about this approach. If each Apache Arrow Flight SQL server implementation uses different custom close action, users can't use a general Apache Arrow Flight SQL client including ADBC to use Apache Arrow Flight SQL servers. (Users need to implement a custom close action for each Apache Arrow Flight SQL server.)

[lidavidm]

I've been working on a set of new proposals for Flight SQL. I think we should address this as part of that.

I don't want us to enforce statefulness if possible, because that runs counter to how gRPC/Flight work. So the server should still be able to deal with clients that do not send the close action.

[lidavidm]

Actually, I think James's proposal already covers this fully: https://lists.apache.org/thread/fd6r1n7vt91sg2c7fr35wcrsqz6x4645

Would you like to follow up there?

[kou]

Thanks! I missed the discussion. I'll reply on the thread.

[kou]

Note: Session timeout instead of closing session explicitly is implemented for now.

[zhjwpku]

I tried this extension and noticed that each executor will last for 5 minutes due to session timeout, I glanced the FlightSqlServerBase class a little bit, if it has a method knows the client's close action, then we can use it to close the executor. Is there any capability in arrow flight that we can use now?

[kou]

No there isn't. We need to forward the discussion referred at https://github.com/apache/arrow-flight-sql-postgresql/issues/13#issuecomment-1424289284 for it. Could you join the discussion on the [email protected] mailing list?

[kou]

Ah, https://github.com/apache/arrow/pull/34817 is a proposed implementation. I thought that it's not related to https://github.com/apache/arrow-flight-sql-postgresql/issues/13#issuecomment-1424289284 discussion.

[cisaacson]

I am interested in this capability for the Rust version of arrow-flight-sql. A timeout would not meet our requirements. I would suggest some type of on_close event that the client calls on the server as it is closing. If I can help please let me know.

[kou]

https://github.com/apache/arrow/pull/34817 has been merged. So we can implement https://arrow.apache.org/docs/format/FlightSql.html#flight-server-session-management for explicit close.

[cisaacson]

Thanks @kou, the CloseSession command is exactly what I was looking for. I have 2 questions:

• Is this implemented for arrow-rs? I do not believe so as CloseSession does not appear in the codebase.
• Is there an example you can point me to?

If I can help with an example I would be happy to do that, for implementing the Rust version it may be better for someone more familiar with the codebase than me.

And thanks for all the work on this.

[cisaacson]

I don't know if this is the right place to report this, but the latest version of master for arrow-rs does not compile:

no associated item named `GRPC_STATUS` found for struct `Status` in the current scope
    --> arrow-flight/src/arrow.flight.protocol.rs:1578:48

If I should post it somewhere else let me know.

[kou]

We need the followings for explicit close:

• Implement CloseSession in https://github.com/apache/arrow-rs
• Implement CloseSession in this repository

Could you report arrow-rs error to https://github.com/apache/arrow-rs/issues ?

[cisaacson]

@kou Sure, I will report it there.

[cisaacson]

This issue can be closed as it has been reported in the arrow-rs project.

[kou]

This issue isn't for arrow-rs. So we should not close this until we implement CloseSession in this repository.