DC Aware Round robin¶

This is a more sophisticated version of Round robin policy. It takes all nodes in the local datacenter and uses them one after another.
If no nodes from the local datacenter are available it will fall back to other nodes.

For example if there are two datacenters:

• us_east with nodes: A, B, C

• us_west with nodes: D, E, F

this policy when set to us_east will only use A, B, C, A, B, …

The policy may still return nodes in remote datacenters in the created plan as a fallback. This behaviour is configurable by the flag with a setter. By default the flag is set. In the example below, the flag is manually unset, which means that remote nodes are not present as a fallback at the end of the plan.

use scylla::{Session, SessionBuilder};
use scylla::transport::load_balancing::DcAwareRoundRobinPolicy;
use std::sync::Arc;

let local_dc_name: String = "us_east".to_string();

let mut policy = DcAwareRoundRobinPolicy::new(local_dc_name);
policy.set_include_remote_nodes(false);

let session: Session = SessionBuilder::new()
    .known_node("127.0.0.1:9042")
    .load_balancing(Arc::new(policy))
    .build()
    .await?;