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use super::{ChildLoadBalancingPolicy, LoadBalancingPolicy, Plan, Statement};
use crate::transport::{cluster::ClusterData, node::Node};
use std::sync::{
atomic::{AtomicUsize, Ordering},
Arc,
};
use tracing::trace;
pub struct RoundRobinPolicy {
index: AtomicUsize,
}
impl RoundRobinPolicy {
pub fn new() -> Self {
Self {
index: AtomicUsize::new(0),
}
}
}
impl Default for RoundRobinPolicy {
fn default() -> Self {
Self::new()
}
}
const ORDER_TYPE: Ordering = Ordering::Relaxed;
impl LoadBalancingPolicy for RoundRobinPolicy {
fn plan<'a>(&self, _statement: &Statement, cluster: &'a ClusterData) -> Plan<'a> {
let index = self.index.fetch_add(1, ORDER_TYPE);
let nodes_count = cluster.all_nodes.len();
let rotation = super::compute_rotation(index, nodes_count);
let rotated_nodes = super::slice_rotated_left(&cluster.all_nodes, rotation).cloned();
trace!(
nodes = rotated_nodes
.clone()
.map(|node| node.address.to_string())
.collect::<Vec<String>>()
.join(",")
.as_str(),
"RoundRobin"
);
Box::new(rotated_nodes)
}
fn name(&self) -> String {
"RoundRobinPolicy".to_string()
}
}
impl ChildLoadBalancingPolicy for RoundRobinPolicy {
fn apply_child_policy(
&self,
mut plan: Vec<Arc<Node>>,
) -> Box<dyn Iterator<Item = Arc<Node>> + Send + Sync> {
let index = self.index.fetch_add(1, ORDER_TYPE);
let len = plan.len();
plan.rotate_left(super::compute_rotation(index, len));
Box::new(plan.into_iter())
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::transport::load_balancing::tests;
use std::collections::HashSet;
#[tokio::test]
async fn test_round_robin_policy() {
let cluster = tests::mock_cluster_data_for_round_robin_tests();
let policy = RoundRobinPolicy::new();
let plans = (0..16)
.map(|_| {
tests::get_plan_and_collect_node_identifiers(
&policy,
&tests::EMPTY_STATEMENT,
&cluster,
)
})
.collect::<HashSet<_>>();
let expected_plans = vec![
vec![1, 2, 3, 4, 5],
vec![2, 3, 4, 5, 1],
vec![3, 4, 5, 1, 2],
vec![4, 5, 1, 2, 3],
vec![5, 1, 2, 3, 4],
]
.into_iter()
.collect::<HashSet<Vec<_>>>();
assert_eq!(expected_plans, plans);
}
}