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Merged
BubbleCal merged 2 commits into from
Dec 2, 2025
Merged

perf: avoid allocating filtered nodes on HNSW search path #5377

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a542930
Optimize HNSW search and benchmarks
BubbleCal Dec 1, 2025
e0629e2
Merge branch 'main' of https://github.com/lancedb/lance into hnsw-per…
BubbleCal Dec 1, 2025
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107 changes: 49 additions & 58 deletions rust/lance-index/benches/hnsw.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,10 +22,10 @@ use lance_linalg::distance::DistanceType;
use lance_testing::datagen::generate_random_array_with_seed;

fn bench_hnsw(c: &mut Criterion) {
const DIMENSION: usize = 512;
const TOTAL: usize = 10 * 1024;
const DIMENSION: usize = 128;
const TOTAL: usize = 100_000;
const SEED: [u8; 32] = [42; 32];
const K: usize = 10;
const K: usize = 100;

let rt = tokio::runtime::Runtime::new().unwrap();

Expand All @@ -34,64 +34,55 @@ fn bench_hnsw(c: &mut Criterion) {
let vectors = Arc::new(FlatFloatStorage::new(fsl.clone(), DistanceType::L2));

let query = fsl.value(0);
c.bench_function(
format!("create_hnsw({TOTAL}x{DIMENSION},levels=6)").as_str(),
|b| {
b.to_async(&rt).iter(|| async {
let hnsw =
HNSW::index_vectors(vectors.as_ref(), HnswBuildParams::default().max_level(6))
.unwrap();
let uids: HashSet<u32> = hnsw
.search_basic(
query.clone(),
K,
&HnswQueryParams {
ef: 300,
lower_bound: None,
upper_bound: None,
dist_q_c: 0.0,
},
None,
vectors.as_ref(),
)
.unwrap()
.iter()
.map(|node| node.id)
.collect();
c.bench_function(format!("create_hnsw({TOTAL}x{DIMENSION})").as_str(), |b| {
b.to_async(&rt).iter(|| async {
let hnsw = HNSW::index_vectors(vectors.as_ref(), HnswBuildParams::default()).unwrap();
let uids: HashSet<u32> = hnsw
.search_basic(
query.clone(),
K,
&HnswQueryParams {
ef: 300,
lower_bound: None,
upper_bound: None,
dist_q_c: 0.0,
},
None,
vectors.as_ref(),
)
.unwrap()
.iter()
.map(|node| node.id)
.collect();

assert_eq!(uids.len(), K);
})
},
);
assert_eq!(uids.len(), K);
})
});

let hnsw =
HNSW::index_vectors(vectors.as_ref(), HnswBuildParams::default().max_level(6)).unwrap();
c.bench_function(
format!("search_hnsw{TOTAL}x{DIMENSION}, levels=6").as_str(),
|b| {
b.to_async(&rt).iter(|| async {
let uids: HashSet<u32> = hnsw
.search_basic(
query.clone(),
K,
&HnswQueryParams {
ef: 300,
lower_bound: None,
upper_bound: None,
dist_q_c: 0.0,
},
None,
vectors.as_ref(),
)
.unwrap()
.iter()
.map(|node| node.id)
.collect();
let hnsw = HNSW::index_vectors(vectors.as_ref(), HnswBuildParams::default()).unwrap();
c.bench_function(format!("search_hnsw{TOTAL}x{DIMENSION}").as_str(), |b| {
b.to_async(&rt).iter(|| async {
let uids: HashSet<u32> = hnsw
.search_basic(
query.clone(),
K,
&HnswQueryParams {
ef: 300,
lower_bound: None,
upper_bound: None,
dist_q_c: 0.0,
},
None,
vectors.as_ref(),
)
.unwrap()
.iter()
.map(|node| node.id)
.collect();

assert_eq!(uids.len(), K);
})
},
);
assert_eq!(uids.len(), K);
})
});
}

#[cfg(target_os = "linux")]
Expand Down
19 changes: 10 additions & 9 deletions rust/lance-index/src/vector/graph.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -181,6 +181,11 @@ impl Visited<'_> {
self.visited[node_id_usize]
}

#[inline(always)]
pub fn iter_ones(&self) -> impl Iterator<Item = usize> + '_ {
self.visited.iter_ones()
}

pub fn count_ones(&self) -> usize {
self.visited.count_ones()
}
Expand Down Expand Up @@ -310,20 +315,15 @@ pub fn beam_search(
if current.dist > furthest && results.len() == k {
break;
}
let neighbors = graph.neighbors(current.id);

let furthest = results
.peek()
.map(|node| node.dist)
.unwrap_or(OrderedFloat(f32::INFINITY));

let unvisited_neighbors: Vec<_> = neighbors
.iter()
.filter(|&&neighbor| !visited.contains(neighbor))
.copied()
.collect();

let process_neighbor = |neighbor: u32| {
if visited.contains(neighbor) {
return;
}
visited.insert(neighbor);
let dist: OrderedFloat = dist_calc.distance(neighbor).into();
if dist <= furthest || results.len() < k {
Expand All @@ -343,8 +343,9 @@ pub fn beam_search(
candidates.push(Reverse((dist, neighbor).into()));
}
};
let neighbors = graph.neighbors(current.id);
process_neighbors_with_look_ahead(
&unvisited_neighbors,
&neighbors,
process_neighbor,
prefetch_distance,
dist_calc,
Expand Down
72 changes: 46 additions & 26 deletions rust/lance-index/src/vector/hnsw/builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ use lance_linalg::distance::DistanceType;
use rayon::prelude::*;
use snafu::location;
use std::cmp::min;
use std::collections::{BinaryHeap, HashMap};
use std::collections::{BinaryHeap, HashMap, VecDeque};
use std::fmt::Debug;
use std::iter;
use std::sync::atomic::{AtomicUsize, Ordering};
Expand Down Expand Up @@ -243,39 +243,59 @@ impl HNSW {
prefilter_bitset: Visited,
params: &HnswQueryParams,
) -> Vec<OrderedNode> {
let node_ids = storage
.row_ids()
.enumerate()
.filter_map(|(node_id, _)| {
prefilter_bitset
.contains(node_id as u32)
.then_some(node_id as u32)
})
.collect_vec();

let lower_bound: OrderedFloat = params.lower_bound.unwrap_or(f32::MIN).into();
let upper_bound: OrderedFloat = params.upper_bound.unwrap_or(f32::MAX).into();

let dist_calc = storage.dist_calculator(query, params.dist_q_c);
let mut heap = BinaryHeap::<OrderedNode>::with_capacity(k);
for i in 0..node_ids.len() {
if let Some(ahead) = self.inner.params.prefetch_distance {
if i + ahead < node_ids.len() {
dist_calc.prefetch(node_ids[i + ahead]);

match self.inner.params.prefetch_distance {
Some(ahead) if ahead > 0 => {
let mut ids_iter = prefilter_bitset.iter_ones().map(|i| i as u32);
let mut buffer = VecDeque::with_capacity(ahead + 1);
for _ in 0..=ahead {
if let Some(id) = ids_iter.next() {
buffer.push_back(id);
} else {
break;
}
}

while let Some(node_id) = buffer.pop_front() {
if let Some(&prefetch_id) = buffer.get(ahead - 1) {
dist_calc.prefetch(prefetch_id);
}
if let Some(next) = ids_iter.next() {
buffer.push_back(next);
}

let dist: OrderedFloat = dist_calc.distance(node_id).into();
if dist <= lower_bound || dist > upper_bound {
continue;
}
if heap.len() < k {
heap.push((dist, node_id).into());
} else if dist < heap.peek().unwrap().dist {
heap.pop();
heap.push((dist, node_id).into());
}
}
}
let node_id = node_ids[i];
let dist: OrderedFloat = dist_calc.distance(node_id).into();
if dist <= lower_bound || dist > upper_bound {
continue;
}
if heap.len() < k {
heap.push((dist, node_id).into());
} else if dist < heap.peek().unwrap().dist {
heap.pop();
heap.push((dist, node_id).into());
_ => {
for node_id in prefilter_bitset.iter_ones().map(|i| i as u32) {
let dist: OrderedFloat = dist_calc.distance(node_id).into();
if dist <= lower_bound || dist > upper_bound {
continue;
}
if heap.len() < k {
heap.push((dist, node_id).into());
} else if dist < heap.peek().unwrap().dist {
heap.pop();
heap.push((dist, node_id).into());
}
}
}
}
};
heap.into_sorted_vec()
}

Expand Down
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