Fix HNSW

TestHNSW/HNSWDemo/Program.cs

@@ -2,13 +2,35 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
-using System.Threading;
 using ZeroLevel.HNSW;
 
 namespace HNSWDemo
 {
     class Program
     {
+        public class VectorsDirectCompare
+        {
+            private readonly IList<float[]> _vectors;
+            private readonly Func<float[], float[], float> _distance;
+
+            public VectorsDirectCompare(List<float[]> vectors, Func<float[], float[], float> distance)
+            {
+                _vectors = vectors;
+                _distance = distance;
+            }
+
+            public IEnumerable<(int, float)> KNearest(float[] v, int k)
+            {
+                var weights = new Dictionary<int, float>();
+                for (int i = 0; i < _vectors.Count; i++)
+                {
+                    var d = _distance(v, _vectors[i]);
+                    weights[i] = d;
+                }
+                return weights.OrderBy(p => p.Value).Take(k).Select(p => (p.Key, p.Value));
+            }
+        }
+
         public enum Gender
         {
             Unknown, Male, Feemale
@@ -77,28 +99,65 @@ namespace HNSWDemo
         static void Main(string[] args)
         {
             var dimensionality = 128;
-            var testCount = 5000;
-            var count = 10000;
-            var batchSize = 1000;
+            var testCount = 1000;
+            var count = 5000;
             var samples = Person.GenerateRandom(dimensionality, count);
 
             var sw = new Stopwatch();
-            var world = new SmallWorld<float[]>(NSWOptions<float[]>.Create(6, 10, 200, 200, CosineDistance.ForUnits, false, false, selectionHeuristic: NeighbourSelectionHeuristic.SelectHeuristic));
 
-            for (int i = 0; i < (count / batchSize); i++)
-            {
-                var batch = samples.Skip(i * batchSize).Take(batchSize).ToArray();
-                sw.Restart();
+            var test = new VectorsDirectCompare(samples.Select(s => s.Item1).ToList(), CosineDistance.ForUnits);
+            var world = new SmallWorld<float[]>(NSWOptions<float[]>.Create(6, 15, 200, 200, CosineDistance.ForUnits, true, true, selectionHeuristic: NeighbourSelectionHeuristic.SelectSimple));
+
+            var batch = samples.ToArray();
+            
             var ids = world.AddItems(batch.Select(i => i.Item1).ToArray());
-                sw.Stop();
-                Console.WriteLine($"Batch [{i}]. Insert {ids.Length} items on {sw.ElapsedMilliseconds} ms");
+            
+            Console.WriteLine($"Insert {ids.Length} items on {sw.ElapsedMilliseconds} ms");
             for (int bi = 0; bi < batch.Length; bi++)
             {
                 _database.Add(ids[bi], batch[bi].Item2);
             }
-            }
 
+            Console.WriteLine("Start test");
+            int K = 200;
             var vectors = RandomVectors(dimensionality, testCount);
+            var totalHits = new List<int>();
+            var timewatchesHNSW = new List<float>();
+            var timewatchesNP = new List<float>();
+            foreach (var v in vectors)
+            {
+                sw.Restart();
+                var gt = test.KNearest(v, K).ToDictionary(p => p.Item1, p => p.Item2);
+                sw.Stop();
+                timewatchesNP.Add(sw.ElapsedMilliseconds);
+
+                sw.Restart();
+                var result = world.Search(v, K);
+                sw.Stop();
+                timewatchesHNSW.Add(sw.ElapsedMilliseconds);
+                var hits = 0;
+                foreach (var r in result)
+                {
+                    if (gt.ContainsKey(r.Item1))
+                    {
+                        hits++;
+                    }
+                }
+                totalHits.Add(hits);
+            }
+            Console.WriteLine($"MIN Accuracity: {totalHits.Min() * 100 / K}%");
+            Console.WriteLine($"AVG Accuracity: {totalHits.Average() * 100 / K}%");
+            Console.WriteLine($"MAX Accuracity: {totalHits.Max() * 100 / K}%");
+
+            Console.WriteLine($"MIN HNSW TIME: {timewatchesHNSW.Min()} ms");
+            Console.WriteLine($"AVG HNSW TIME: {timewatchesHNSW.Average()} ms");
+            Console.WriteLine($"MAX HNSW TIME: {timewatchesHNSW.Max()} ms");
+
+            Console.WriteLine($"MIN NP TIME: {timewatchesNP.Min()} ms");
+            Console.WriteLine($"AVG NP TIME: {timewatchesNP.Average()} ms");
+            Console.WriteLine($"MAX NP TIME: {timewatchesNP.Max()} ms");
+
+
 
             //HNSWFilter filter = new HNSWFilter(ids => ids.Where(id => { var p = _database[id]; return p.Age > 45 && p.Gender == Gender.Feemale; }));
 

ZeroLevel.HNSW/Layer.cs

@@ -16,7 +16,7 @@ namespace ZeroLevel.HNSW
         /// <summary>
         /// Count nodes at layer
         /// </summary>
-        public int Count => (_links.Count >> 1);
+        public int CountLinks => (_links.Count);
 
         public Layer(NSWOptions<TItem> options, VectorSet<TItem> vectors)
         {
@@ -24,13 +24,13 @@ namespace ZeroLevel.HNSW
             _vectors = vectors;
         }
 
-        public void AddBidirectionallConnectionts(int q, int p, float qpDistance)
+        public void AddBidirectionallConnectionts(int q, int p, float qpDistance, bool isMapLayer)
         {
             // поиск в ширину ближайших узлов к найденному
             var nearest = _links.FindLinksForId(p).ToArray();
             // если у найденного узла максимальное количество связей
             // if │eConn│ > Mmax // shrink connections of e
-            if (nearest.Length >= _options.M)
+            if (nearest.Length >= (isMapLayer ? _options.M * 2 : _options.M))
             {
                 // ищем связь с самой большой дистанцией
                 float distance = nearest[0].Item3;
@@ -55,6 +55,12 @@ namespace ZeroLevel.HNSW
             }
         }
 
+        public void Append(int q)
+        {
+            _links.Add(q, q, 0);
+        }
+
+
         #region Implementation of https://arxiv.org/ftp/arxiv/papers/1603/1603.09320.pdf
         /// <summary>
         /// Algorithm 2

ZeroLevel.HNSW/Services/CompactBiDirectionalLinksSet.cs

@@ -43,7 +43,9 @@ namespace ZeroLevel.HNSW
             {
                 _set.Remove(k1old);
                 _set.Remove(k2old);
+                if (!_set.ContainsKey(k1new))
                     _set.Add(k1new, distance);
+                if (!_set.ContainsKey(k2new))
                     _set.Add(k2new, distance);
             }
             finally

ZeroLevel.HNSW/SmallWorld.cs

@@ -7,7 +7,7 @@ namespace ZeroLevel.HNSW
 {
     public class ProbabilityLayerNumberGenerator
     {
-        private const float DIVIDER = 4.362f;
+        private const float DIVIDER = 3.361f;
         private readonly float[] _probabilities;
 
         public ProbabilityLayerNumberGenerator(int maxLayers, int M)
@@ -38,11 +38,8 @@ namespace ZeroLevel.HNSW
         private readonly NSWOptions<TItem> _options;
         private readonly VectorSet<TItem> _vectors;
         private readonly Layer<TItem>[] _layers;
-
-        private Layer<TItem> EnterPointsLayer => _layers[_layers.Length - 1];
-        private Layer<TItem> LastLayer => _layers[0];
-        private int EntryPoint = -1;
-        private int MaxLayer = -1;
+        private int EntryPoint = 0;
+        private int MaxLayer = 0;
         private readonly ProbabilityLayerNumberGenerator _layerLevelGenerator;
         private ReaderWriterLockSlim _lockGraph = new ReaderWriterLockSlim();
 
@@ -58,9 +55,12 @@ namespace ZeroLevel.HNSW
             }
         }
 
-        public IEnumerable<(int, TItem[])> Search(TItem vector, int k, HashSet<int> activeNodes = null)
+        public IEnumerable<(int, TItem, float)> Search(TItem vector, int k, HashSet<int> activeNodes = null)
+        {
+            foreach (var pair in KNearest(vector, k))
             {
-            return Enumerable.Empty<(int, TItem[])>();
+                yield return (pair.Item1, _vectors[pair.Item1], pair.Item2);
+            }
         }
 
         public int[] AddItems(IEnumerable<TItem> vectors)
@@ -109,24 +109,25 @@ namespace ZeroLevel.HNSW
         public void INSERT(int q)
         {
             var distance = new Func<int, float>(candidate => _options.Distance(_vectors[q], _vectors[candidate]));
-
             // W ← ∅ // list for the currently found nearest elements
             IDictionary<int, float> W = new Dictionary<int, float>();
             // ep ← get enter point for hnsw
-            var ep = EntryPoint == -1 ? 0 : EntryPoint;
-            var epDist = 0.0f;
+            var ep = EntryPoint;
+            var epDist = distance(ep);
             // L ← level of ep // top layer for hnsw
             var L = MaxLayer;
             // l ← ⌊-ln(unif(0..1))∙mL⌋ // new element’s level            
             int l = _layerLevelGenerator.GetRandomLayer();            
-            if (L == -1)
-            {
-                L = l;
-                MaxLayer = l;
-            }
             // for lc ← L … l+1
             // Проход с верхнего уровня до уровня где появляется элемент, для нахождения точки входа
             for (int lc = L; lc > l; --lc)
+            {
+                if (_layers[lc].CountLinks == 0)
+                {
+                    _layers[lc].Append(q);
+                    ep = q;
+                }
+                else
                 {
                     // W ← SEARCH-LAYER(q, ep, ef = 1, lc)
                     _layers[lc].RunKnnAtLayer(ep, distance, W, 1);
@@ -136,20 +137,28 @@ namespace ZeroLevel.HNSW
                     epDist = nearest.Value;
                     W.Clear();
                 }
+            }
             //for lc ← min(L, l) … 0
             // connecting new node to the small world
             for (int lc = Math.Min(L, l); lc >= 0; --lc)
+            {
+                if (_layers[lc].CountLinks == 0)
+                {
+                    _layers[lc].Append(q);
+                    ep = q;
+                }
+                else
                 {
                     // W ← SEARCH - LAYER(q, ep, efConstruction, lc)
                     _layers[lc].RunKnnAtLayer(ep, distance, W, _options.EFConstruction);
                     // neighbors ← SELECT-NEIGHBORS(q, W, M, lc) // alg. 3 or alg. 4
-                var neighbors = SelectBestForConnecting(lc, distance, W);;
+                    var neighbors = SelectBestForConnecting(lc, distance, W);
                     // add bidirectionall connectionts from neighbors to q at layer lc
                     // for each e ∈ neighbors // shrink connections if needed
                     foreach (var e in neighbors)
                     {
                         // eConn ← neighbourhood(e) at layer lc
-                    _layers[lc].AddBidirectionallConnectionts(q, e.Key, e.Value);
+                        _layers[lc].AddBidirectionallConnectionts(q, e.Key, e.Value, lc == 0);
                         // if distance from newNode to newNeighbour is better than to bestPeer => update bestPeer
                         if (e.Value < epDist)
                         {
@@ -161,6 +170,7 @@ namespace ZeroLevel.HNSW
                     ep = W.OrderBy(p => p.Value).First().Key;
                     W.Clear();
                 }
+            }
             // if l > L
             if (l > L)
             {