sql: ALTER ROLE ... SET tracing=on; crashes the database

[Xiang-Gu]

Describe the problem

CREATE USER roacher;
ALTER ROLE roacher SET tracing = 'on';

crashes the database with message:

invalid syntax: statement ignored: unexpected error: driver: bad connection
warning: connection lost!
opening new connection: all session settings will be lost
warning: error retrieving the transaction status: dial tcp [::1]:26257: connect: connection refused
warning: connection lost!
opening new connection: all session settings will be lost
warning: error retrieving the database name: dial tcp [::1]:26257: connect: connection refused
root@localhost:26257/? ?>

Jira issue: CRDB-15203

[rafiss]

I think we probably should disallow setting tracing using ALTER ROLE SET. this variable has special handling, from 61a9676

I noticed that SET LOCAL tracing = 'on; also crashes the database. that might need to be implemented in full.