Function mz_balancerd::cancel_request

pub(crate) async fn cancel_request(
    conn_id: u32,
    secret_key: u32,
    cancellation_resolver: &PathBuf,
)

Broadcasts cancellation to all matching environmentds. conn_id’s bits [31..20] are the lower 12 bits of a UUID for an environmentd/organization. Using that and the template in cancellation_resolver we generate a hostname. That hostname resolves to all IPs of envds that match the UUID (cloud k8s infrastructure maintains that mapping). This function creates a new task for each envd and relays the cancellation message to it, broadcasting it to any envd that might match the connection.

This function returns after it has spawned the tasks, and does not wait for them to complete. This is acceptable because cancellation in the Postgres protocol is best effort and has no guarantees.

The safety of broadcasting this is due to the various randomness in the connection id and secret key, which must match exactly in order to execute a query cancellation. The connection id has 19 bits of randomness, and the secret key the full 32, for a total of 51 bits. That is more than 2e15 combinations, enough to nearly certainly prevent two different envds generating identical combinations.