Timeout support for MySQL and Postgres channel

[sunng87]

What problem does the new feature solve?

Add variables to MySQL and Postgres for controlling statement execution timeout.

This is also a compatibility requirement from Sigma.

What does the feature do?

For MySQL protocol, we need to support SET MAX_EXECUTION_TIME = 5000: https://dev.mysql.com/doc/refman/8.4/en/server-system-variables.html#sysvar_max_execution_time

For Postgres protocol, we need to support SET statement_timeout TO 5000: https://www.postgresql.org/docs/current/runtime-config-client.html#GUC-STATEMENT-TIMEOUT

Implementation challenges

No response

[lyang24]

This looks interesting. I wonder are timeout settings per session? I am trying to measure the scope of the work, do we have similar session variable implementation examples on the codebase?

[sunng87]

@lyang24 good to hear. Yes this variable is session-scoped like our time zone setting. You can check src/session/src/lib.rs as the start for timezone impl, including how we set and how we use it.

[lyang24]

Thanks for the code pointers. may i take this issue?

[sunng87]

Sure