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Skip an allocation in our hot path #1250

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Skip an allocation in our hot path #1250

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5 changes: 3 additions & 2 deletions pgdog/src/backend/pool/lb/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -348,8 +348,9 @@ impl LoadBalancer {
async fn get_internal(&self, request: &Request) -> Result<Guard, Error> {
use LoadBalancingStrategy::*;
use ReadWriteSplit::*;
use smallvec::SmallVec;

let mut candidates: Vec<&Target> = self
let mut candidates: SmallVec<[&Target; 32]> = self
.targets
.iter()
.filter(|target| !target.pool.config().resharding_only) // Don't let reads on resharding-only replicas.
Expand Down Expand Up @@ -384,7 +385,7 @@ impl LoadBalancer {
Random => candidates.shuffle(&mut rand::rng()),
RoundRobin => {
let first = self.round_robin.fetch_add(1, Ordering::Relaxed) % candidates.len();
let mut reshuffled = vec![];
let mut reshuffled = SmallVec::with_capacity(candidates.len());

@levkk levkk Jul 21, 2026

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Literally had to look up the code to understand that it infers the size of the new vec from the type of the original. This is legit a cool lib and a really cool use of the type system.

@sgrif sgrif Jul 21, 2026

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Yeah, it's wild that they managed to make this work before const generics (2.0 uses const generics but it's still alpha)

reshuffled.extend_from_slice(&candidates[first..]);
reshuffled.extend_from_slice(&candidates[..first]);
candidates = reshuffled;
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