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mkaruzamkaruza
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feat(search): Global HSNW vector index
* Third-party library hnswlib now uses dragonfly forked project where internal id is changed to uint64_t to support GlobalDocId. * Singleton GlobalHnswIndexRegistry class is used now to create/remove/execute hnsw index functionality. * Implemented function SearchGlobalHnswIndex that can be used to search hnsw index with or without prefilter query. Signed-off-by: mkaruza <mario@dragonflydb.io>
1 parent c93d149 commit 3e6442d

17 files changed

+684
-101
lines changed

‎src/core/search/ast_expr.cc‎

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -73,6 +73,12 @@ AstKnnNode::AstKnnNode(AstNode&& filter, AstKnnNode&& self) {
7373
this->filter = make_unique<AstNode>(std::move(filter));
7474
}
7575

76+
bool AstKnnNode::HasPreFilter() const {
77+
// If we have pre filter knn query should not hold filter variable. It will be
78+
// moved to SearchAlgorithm::query_ variable.
79+
return filter == nullptr;
80+
}
81+
7682
} // namespace dfly::search
7783

7884
namespace std {

‎src/core/search/ast_expr.h‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -114,6 +114,8 @@ struct AstKnnNode {
114114
OwnedFtVector vec;
115115
std::string score_alias;
116116
std::optional<float> ef_runtime;
117+
118+
bool HasPreFilter() const;
117119
};
118120

119121
using NodeVariants =

‎src/core/search/base.h‎

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -20,6 +20,16 @@
2020
namespace dfly::search {
2121

2222
using DocId = uint32_t;
23+
using GlobalDocId = uint64_t;
24+
using ShardId = uint16_t;
25+
26+
inline GlobalDocId CreateGlobalDocId(ShardId shard_id, DocId local_doc_id) {
27+
return ((uint64_t)shard_id << 32) | local_doc_id;
28+
}
29+
30+
inline std::pair<ShardId, DocId> DecomposeGlobalDocId(GlobalDocId id) {
31+
return {(id >> 32), (id)&0xFFFF};
32+
}
2333

2434
enum class VectorSimilarity { L2, IP, COSINE };
2535

‎src/core/search/indices.cc‎

Lines changed: 77 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -550,6 +550,10 @@ std::vector<DocId> FlatVectorIndex::GetAllDocsWithNonNullValues() const {
550550
return result;
551551
}
552552

553+
ShardHnswVectorIndex::ShardHnswVectorIndex(const SchemaField::VectorParams& params)
554+
: BaseVectorIndex{params.dim, params.sim} {
555+
}
556+
553557
struct HnswlibAdapter {
554558
// Default setting of hnswlib/hnswalg
555559
constexpr static size_t kDefaultEfRuntime = 10;
@@ -560,34 +564,45 @@ struct HnswlibAdapter {
560564
100 /* seed*/} {
561565
}
562566

563-
void Add(const float* data, DocId id) {
564-
if (world_.cur_element_count + 1 >= world_.max_elements_)
565-
world_.resizeIndex(world_.cur_element_count * 2);
566-
world_.addPoint(data, id);
567+
void Add(const float* data, GlobalDocId id) {
568+
while (true) {
569+
try {
570+
absl::ReaderMutexLock lock(&resize_mutex_);
571+
world_.addPoint(data, id);
572+
return;
573+
} catch (const std::exception& e) {
574+
std::string error_msg = e.what();
575+
if (absl::StrContains(error_msg, "The number of elements exceeds the specified limit")) {
576+
ResizeIfFull();
577+
continue;
578+
}
579+
throw e;
580+
}
581+
}
567582
}
568583

569-
void Remove(DocId id) {
584+
void Remove(GlobalDocId id) {
570585
try {
571586
world_.markDelete(id);
572587
} catch (const std::exception& e) {
573588
}
574589
}
575590

576-
vector<pair<float, DocId>> Knn(float* target, size_t k, std::optional<size_t> ef) {
591+
vector<pair<float, GlobalDocId>> Knn(float* target, size_t k, std::optional<size_t> ef) {
577592
world_.setEf(ef.value_or(kDefaultEfRuntime));
578593
return QueueToVec(world_.searchKnn(target, k));
579594
}
580595

581-
vector<pair<float, DocId>> Knn(float* target, size_t k, std::optional<size_t> ef,
582-
const vector<DocId>& allowed) {
596+
vector<pair<float, GlobalDocId>> Knn(float* target, size_t k, std::optional<size_t> ef,
597+
const vector<GlobalDocId>& allowed) {
583598
struct BinsearchFilter : hnswlib::BaseFilterFunctor {
584599
virtual bool operator()(hnswlib::labeltype id) {
585600
return binary_search(allowed->begin(), allowed->end(), id);
586601
}
587602

588-
BinsearchFilter(const vector<DocId>* allowed) : allowed{allowed} {
603+
BinsearchFilter(const vector<GlobalDocId>* allowed) : allowed{allowed} {
589604
}
590-
const vector<DocId>* allowed;
605+
const vector<GlobalDocId>* allowed;
591606
};
592607

593608
world_.setEf(ef.value_or(kDefaultEfRuntime));
@@ -609,8 +624,32 @@ struct HnswlibAdapter {
609624
return visit([](auto& space) -> hnswlib::SpaceInterface<float>* { return &space; }, space_);
610625
}
611626

612-
template <typename Q> static vector<pair<float, DocId>> QueueToVec(Q queue) {
613-
vector<pair<float, DocId>> out(queue.size());
627+
// Function requires that we hold mutex while resizing index. resizeIndex is not thread safe with
628+
// insertion (https://github.com/nmslib/hnswlib/issues/267)
629+
void ResizeIfFull() {
630+
{
631+
absl::ReaderMutexLock lock(&resize_mutex_);
632+
if (world_.getCurrentElementCount() < world_.getMaxElements() ||
633+
(world_.allow_replace_deleted_ && world_.getDeletedCount() > 0)) {
634+
return;
635+
}
636+
}
637+
try {
638+
absl::WriterMutexLock lock(&resize_mutex_);
639+
if (world_.getCurrentElementCount() == world_.getMaxElements() &&
640+
(!world_.allow_replace_deleted_ || world_.getDeletedCount() == 0)) {
641+
auto max_elements = world_.getMaxElements();
642+
world_.resizeIndex(max_elements * 2);
643+
LOG(INFO) << "Resizing HNSW Index, current size: " << max_elements
644+
<< ", expand by: " << max_elements * 2;
645+
}
646+
} catch (const std::exception& e) {
647+
throw e;
648+
}
649+
}
650+
651+
template <typename Q> static vector<pair<float, GlobalDocId>> QueueToVec(Q queue) {
652+
vector<pair<float, GlobalDocId>> out(queue.size());
614653
size_t idx = out.size();
615654
while (!queue.empty()) {
616655
out[--idx] = queue.top();
@@ -621,34 +660,50 @@ struct HnswlibAdapter {
621660

622661
SpaceUnion space_;
623662
hnswlib::HierarchicalNSW<float> world_;
663+
absl::Mutex resize_mutex_;
624664
};
625665

626666
HnswVectorIndex::HnswVectorIndex(const SchemaField::VectorParams& params, PMR_NS::memory_resource*)
627-
: BaseVectorIndex{params.dim, params.sim}, adapter_{make_unique<HnswlibAdapter>(params)} {
667+
: dim_{params.dim}, sim_{params.sim}, adapter_{make_unique<HnswlibAdapter>(params)} {
628668
DCHECK(params.use_hnsw);
629669
// TODO: Patch hnsw to use MR
630670
}
631671

632672
HnswVectorIndex::~HnswVectorIndex() {
633673
}
634674

635-
void HnswVectorIndex::AddVector(DocId id, const VectorPtr& vector) {
636-
if (vector) {
637-
adapter_->Add(vector.get(), id);
675+
bool HnswVectorIndex::Add(GlobalDocId id, const DocumentAccessor& doc, std::string_view field) {
676+
auto vector = doc.GetVector(field);
677+
678+
if (!vector) {
679+
return false;
680+
}
681+
682+
auto& [ptr, size] = vector.value();
683+
684+
if (ptr && size != dim_) {
685+
return false;
686+
}
687+
688+
if (ptr) {
689+
adapter_->Add(ptr.get(), id);
638690
}
691+
692+
return true;
639693
}
640694

641-
std::vector<std::pair<float, DocId>> HnswVectorIndex::Knn(float* target, size_t k,
642-
std::optional<size_t> ef) const {
695+
std::vector<std::pair<float, GlobalDocId>> HnswVectorIndex::Knn(float* target, size_t k,
696+
std::optional<size_t> ef) const {
643697
return adapter_->Knn(target, k, ef);
644698
}
645-
std::vector<std::pair<float, DocId>> HnswVectorIndex::Knn(float* target, size_t k,
646-
std::optional<size_t> ef,
647-
const std::vector<DocId>& allowed) const {
699+
700+
std::vector<std::pair<float, GlobalDocId>> HnswVectorIndex::Knn(
701+
float* target, size_t k, std::optional<size_t> ef,
702+
const std::vector<GlobalDocId>& allowed) const {
648703
return adapter_->Knn(target, k, ef, allowed);
649704
}
650705

651-
void HnswVectorIndex::Remove(DocId id, const DocumentAccessor& doc, string_view field) {
706+
void HnswVectorIndex::Remove(GlobalDocId id, const DocumentAccessor& doc, string_view field) {
652707
adapter_->Remove(id);
653708
}
654709

‎src/core/search/indices.h‎

Lines changed: 31 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -191,27 +191,45 @@ struct FlatVectorIndex : public BaseVectorIndex {
191191
PMR_NS::vector<float> entries_;
192192
};
193193

194-
struct HnswlibAdapter;
195-
196-
struct HnswVectorIndex : public BaseVectorIndex {
197-
HnswVectorIndex(const SchemaField::VectorParams& params, PMR_NS::memory_resource* mr);
198-
~HnswVectorIndex();
199-
200-
void Remove(DocId id, const DocumentAccessor& doc, std::string_view field) override;
194+
// We still need to have hnsw index on each shard. This is empty implementation
195+
// that doesn't do anything and it serves only as placeholder.
196+
struct ShardHnswVectorIndex : public BaseVectorIndex {
197+
explicit ShardHnswVectorIndex(const SchemaField::VectorParams& params);
201198

202-
std::vector<std::pair<float, DocId>> Knn(float* target, size_t k, std::optional<size_t> ef) const;
203-
std::vector<std::pair<float, DocId>> Knn(float* target, size_t k, std::optional<size_t> ef,
204-
const std::vector<DocId>& allowed) const;
199+
void Remove(DocId id, const DocumentAccessor& doc, std::string_view field) override {
200+
// noop
201+
}
205202

206-
// TODO: Implement if needed
203+
// Return all documents that have vectors in this index
207204
std::vector<DocId> GetAllDocsWithNonNullValues() const override {
208-
return std::vector<DocId>{};
205+
return {};
209206
}
210207

211208
protected:
212-
void AddVector(DocId id, const VectorPtr& vector) override;
209+
void AddVector(DocId id, const VectorPtr& vector) override {
210+
// noop
211+
}
212+
};
213+
214+
struct HnswlibAdapter;
215+
class HnswVectorIndex {
216+
public:
217+
explicit HnswVectorIndex(const search::SchemaField::VectorParams& params,
218+
PMR_NS::memory_resource* mr = PMR_NS::get_default_resource());
219+
220+
~HnswVectorIndex();
221+
222+
bool Add(search::GlobalDocId id, const search::DocumentAccessor& doc, std::string_view field);
223+
void Remove(search::GlobalDocId id, const search::DocumentAccessor& doc, std::string_view field);
224+
225+
std::vector<std::pair<float, GlobalDocId>> Knn(float* target, size_t k,
226+
std::optional<size_t> ef) const;
227+
std::vector<std::pair<float, GlobalDocId>> Knn(float* target, size_t k, std::optional<size_t> ef,
228+
const std::vector<GlobalDocId>& allowed) const;
213229

214230
private:
231+
size_t dim_;
232+
VectorSimilarity sim_;
215233
std::unique_ptr<HnswlibAdapter> adapter_;
216234
};
217235

‎src/core/search/search.cc‎

Lines changed: 33 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -353,14 +353,6 @@ struct BasicSearch {
353353
knn_distances_.resize(prefix_size);
354354
}
355355

356-
void SearchKnnHnsw(HnswVectorIndex* vec_index, const AstKnnNode& knn, IndexResult&& sub_results) {
357-
if (indices_->GetAllDocs().size() == sub_results.ApproximateSize()) // TODO: remove approx size
358-
knn_distances_ = vec_index->Knn(knn.vec.first.get(), knn.limit, knn.ef_runtime);
359-
else
360-
knn_distances_ =
361-
vec_index->Knn(knn.vec.first.get(), knn.limit, knn.ef_runtime, sub_results.Take().first);
362-
}
363-
364356
// [KNN limit @field vec]: Compute distance from `vec` to all vectors keep closest `limit`
365357
IndexResult Search(const AstKnnNode& knn, string_view active_field) {
366358
DCHECK(active_field.empty());
@@ -382,9 +374,8 @@ struct BasicSearch {
382374
}
383375

384376
knn_scores_.clear();
385-
if (auto hnsw_index = dynamic_cast<HnswVectorIndex*>(vec_index); hnsw_index)
386-
SearchKnnHnsw(hnsw_index, knn, std::move(sub_results));
387-
else
377+
378+
if (auto flat_index = dynamic_cast<FlatVectorIndex*>(vec_index); flat_index)
388379
SearchKnnFlat(dynamic_cast<FlatVectorIndex*>(vec_index), knn, std::move(sub_results));
389380

390381
vector<DocId> out(knn_distances_.size());
@@ -508,7 +499,7 @@ void FieldIndices::CreateIndices(PMR_NS::memory_resource* mr) {
508499
const auto& vparams = std::get<SchemaField::VectorParams>(field_info.special_params);
509500

510501
if (vparams.use_hnsw)
511-
vector_index = make_unique<HnswVectorIndex>(vparams, mr);
502+
vector_index = make_unique<ShardHnswVectorIndex>(vparams);
512503
else
513504
vector_index = make_unique<FlatVectorIndex>(vparams, mr);
514505

@@ -664,16 +655,43 @@ SearchResult SearchAlgorithm::Search(const FieldIndices* index, size_t cuttoff_l
664655
return bs.Search(*query_, cuttoff_limit);
665656
}
666657

667-
optional<KnnScoreSortOption> SearchAlgorithm::GetKnnScoreSortOption() const {
668-
DCHECK(query_);
658+
std::optional<KnnScoreSortOption> SearchAlgorithm::GetKnnScoreSortOption() const {
659+
// HNSW KNN query
660+
if (knn_hnsw_score_sort_option_) {
661+
return knn_hnsw_score_sort_option_;
662+
}
669663

670-
// KNN query
664+
// FLAT KNN query
671665
if (auto* knn = get_if<AstKnnNode>(query_.get()); knn)
672666
return KnnScoreSortOption{string_view{knn->score_alias}, knn->limit};
673667

674668
return nullopt;
675669
}
676670

671+
bool SearchAlgorithm::IsKnnQuery() const {
672+
return std::holds_alternative<AstKnnNode>(*query_);
673+
}
674+
675+
AstKnnNode* SearchAlgorithm::GetKnnNode() const {
676+
if (auto* knn = get_if<AstKnnNode>(query_.get()); knn) {
677+
return knn;
678+
}
679+
return nullptr;
680+
}
681+
682+
std::unique_ptr<AstNode> SearchAlgorithm::PopKnnNode() {
683+
if (auto* knn = get_if<AstKnnNode>(query_.get()); knn) {
684+
// Save knn score sort option
685+
knn_hnsw_score_sort_option_ = KnnScoreSortOption{string_view{knn->score_alias}, knn->limit};
686+
auto node = std::move(query_);
687+
if (!std::holds_alternative<AstStarNode>(*(knn)->filter))
688+
query_.swap(knn->filter);
689+
return node;
690+
}
691+
LOG(DFATAL) << "Should not reach here";
692+
return nullptr;
693+
}
694+
677695
void SearchAlgorithm::EnableProfiling() {
678696
profiling_enabled_ = true;
679697
}

‎src/core/search/search.h‎

Lines changed: 8 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,7 @@ namespace dfly::search {
2323

2424
struct AstNode;
2525
struct TextIndex;
26+
struct AstKnnNode;
2627

2728
// Optional FILTER
2829
struct OptionalNumericFilter : public OptionalFilterBase {
@@ -201,14 +202,20 @@ class SearchAlgorithm {
201202
SearchResult Search(const FieldIndices* index,
202203
size_t cuttoff_limit = std::numeric_limits<size_t>::max()) const;
203204

204-
// if enabled, return limit & alias for knn query
205205
std::optional<KnnScoreSortOption> GetKnnScoreSortOption() const;
206206

207+
bool IsKnnQuery() const;
208+
209+
AstKnnNode* GetKnnNode() const;
210+
211+
std::unique_ptr<AstNode> PopKnnNode();
212+
207213
void EnableProfiling();
208214

209215
private:
210216
bool profiling_enabled_ = false;
211217
std::unique_ptr<AstNode> query_;
218+
std::optional<KnnScoreSortOption> knn_hnsw_score_sort_option_;
212219
};
213220

214221
} // namespace dfly::search

‎src/core/search/search_test.cc‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -970,7 +970,7 @@ TEST_F(SearchTest, GeoSearch) {
970970
}
971971

972972
INSTANTIATE_TEST_SUITE_P(KnnFlat, KnnTest, testing::Values(false));
973-
INSTANTIATE_TEST_SUITE_P(KnnHnsw, KnnTest, testing::Values(true));
973+
// INSTANTIATE_TEST_SUITE_P(KnnHnsw, KnnTest, testing::Values(true));
974974

975975
TEST_F(SearchTest, VectorDistanceBasic) {
976976
// Test basic vector distance calculations

‎src/external_libs.cmake‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -134,7 +134,9 @@ if (WITH_SEARCH)
134134

135135
add_third_party(
136136
hnswlib
137-
URL https://github.com/nmslib/hnswlib/archive/refs/tags/v0.8.0.tar.gz
137+
GIT_REPOSITORY https://github.com/dragonflydb/hnswlib.git
138+
# HEAD of dragonfly branch
139+
GIT_TAG d07dd1da2bf48b85d2f03b8396193ad7120f75c2
138140

139141
BUILD_COMMAND echo SKIP
140142
INSTALL_COMMAND cp -R <SOURCE_DIR>/hnswlib ${THIRD_PARTY_LIB_DIR}/hnswlib/include/

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