Fix duplicate results for Knn search

.github/workflows/build.yml

@@ -71,6 +71,7 @@ jobs:
           ./searchKnnWithFilter_test
           ./multiThreadLoad_test
           ./multiThread_replace_test
+          ./replaceSameLabel_test
           ./test_updates
           ./test_updates update
           ./repair_test

CMakeLists.txt

@@ -51,6 +51,9 @@ if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
     add_executable(multiThread_replace_test tests/cpp/multiThread_replace_test.cpp)
     target_link_libraries(multiThread_replace_test hnswlib)
 
+    add_executable(replaceSameLabel_test tests/cpp/replaceSameLabel_test.cpp)
+    target_link_libraries(replaceSameLabel_test hnswlib)
+
     add_executable(main tests/cpp/main.cpp tests/cpp/sift_1b.cpp)
     target_link_libraries(main hnswlib)
 

hnswlib/hnswalg.h

@@ -884,7 +884,14 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
             setExternalLabel(internal_id_replaced, label);
 
             std::unique_lock <std::mutex> lock_table(label_lookup_lock);
-            label_lookup_.erase(label_replaced);
+            // check if the label is already in the index
+            if (label_lookup_.find(label) != label_lookup_.end() && !isMarkedDeleted(label_lookup_[label])) {
+                markDeletedInternal(label_lookup_[label]);
+            }
+            auto label_replaced_lookup = label_lookup_.find(label_replaced);
+            if(label_replaced_lookup != label_lookup_.end() && label_replaced_lookup->second == internal_id_replaced) {
+                label_lookup_.erase(label_replaced);
+            }
             label_lookup_[label] = internal_id_replaced;
             lock_table.unlock();
 

tests/cpp/replaceSameLabel_test.cpp

@@ -0,0 +1,80 @@
+#include "../../hnswlib/hnswlib.h"
+#include <thread>
+#include <chrono>
+#include <iomanip>
+
+int main() {
+    std::cout << "Running replace same label back-to-back test" << std::endl;
+    int d = 16;
+    int num_elements = 50;
+    int max_elements = 2 * num_elements;
+
+    std::mt19937 rng;
+    rng.seed(47);
+    std::uniform_real_distribution<> distrib_real;
+    std::uniform_int_distribution<> distrib_int(0, max_elements - 1);
+
+    hnswlib::InnerProductSpace space(d);
+
+    std::cout << "Generating random data" << std::endl;
+    std::cout << "Initial batch size: " << max_elements << std::endl;
+    float* initial_batch = new float[d * max_elements];
+    for (int i = 0; i < d * max_elements; i++) {
+        initial_batch[i] = distrib_real(rng);
+    }
+
+    std::cout << "Update batch size: " << num_elements << std::endl;
+    float* update_batch = new float[d * num_elements];
+    for (int i = 0; i < d * num_elements; i++) {
+        update_batch[i] = distrib_real(rng);
+    }
+
+    std::cout << "Building index" << std::endl;
+    hnswlib::HierarchicalNSW<float>* alg_hnsw = new hnswlib::HierarchicalNSW<float>(&space, 1024, 16, 200, 456, true);
+
+    std::vector<int> labels;
+
+    std::cout << "Adding initial batch" << std::endl;
+    for(int row = 0; row < max_elements; row++) {
+        int label = distrib_int(rng);
+        labels.push_back(label);
+        alg_hnsw->addPoint((void*)(initial_batch + d * row), label, true);
+    };
+
+    std::cout << "Deleting half of the initial batch" << std::endl;
+    for (int i = 0; i < labels.size() / 2; i++) {
+        if(!alg_hnsw->isMarkedDeleted(alg_hnsw->label_lookup_[labels[i]]))
+            alg_hnsw->markDelete(labels[i]);
+    }
+
+    std::cout << "Updating index size" << std::endl;
+    size_t curr_ele_count = alg_hnsw->getCurrentElementCount();
+    if(curr_ele_count + max_elements > alg_hnsw->getMaxElements()) {
+            alg_hnsw->resizeIndex((curr_ele_count + max_elements) * 1.3);
+    }
+
+    std::cout << "Adding update batch" << std::endl;
+    for(int row; row < num_elements; row++) {
+        alg_hnsw->addPoint((void*)(update_batch + d * row), 42, true);
+    };
+
+
+    std::cout << "Searching for 10 nearest neighbors" << std::endl;
+    auto results = alg_hnsw->searchKnnCloserFirst((void*)(initial_batch), 10);
+
+    // check if the search results contain duplicate labels
+    std::cout << "Checking search results for duplicate labels" << std::endl;
+    std::unordered_set<int> labels_set;
+    for (int i = 0; i < results.size(); i++) {
+        labels_set.insert(results[i].second);
+    }
+    if (labels_set.size() != 10) {
+        std::cout << "Search results contain duplicate labels" << std::endl;
+        throw std::runtime_error("Search results contain duplicate labels");
+    }
+
+    delete[] initial_batch;
+    delete[] update_batch;
+    delete alg_hnsw;
+    return 0;
+}