PosgreSQL hybrid search

extensions/Postgres/Postgres.TestApplication/Program.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using Microsoft.KernelMemory;
+using Microsoft.KernelMemory.AI.Ollama;
 using Microsoft.KernelMemory.DocumentStorage.DevTools;
 using Microsoft.KernelMemory.FileSystem.DevTools;
 
@@ -26,16 +27,13 @@ private static async Task Test1()
         var postgresConfig = cfg.GetSection("KernelMemory:Services:Postgres").Get<PostgresConfig>();
         ArgumentNullExceptionEx.ThrowIfNull(postgresConfig, nameof(postgresConfig), "Postgres config not found");
 
-        var azureOpenAIEmbeddingConfig = cfg.GetSection("KernelMemory:Services:AzureOpenAIEmbedding").Get<AzureOpenAIConfig>();
-        ArgumentNullExceptionEx.ThrowIfNull(azureOpenAIEmbeddingConfig, nameof(azureOpenAIEmbeddingConfig), "AzureOpenAIEmbedding config not found");
-
-        var azureOpenAITextConfig = cfg.GetSection("KernelMemory:Services:AzureOpenAIText").Get<AzureOpenAIConfig>();
-        ArgumentNullExceptionEx.ThrowIfNull(azureOpenAITextConfig, nameof(azureOpenAITextConfig), "AzureOpenAIText config not found");
+        var ollamaConfig = cfg.GetSection("KernelMemory:Services:Ollama").Get<OllamaConfig>();
+        ArgumentNullExceptionEx.ThrowIfNull(ollamaConfig, nameof(ollamaConfig), "Ollama config not found");
 
         // Concatenate our 'WithPostgresMemoryDb()' after 'WithOpenAIDefaults()' from the core nuget
         var mem1 = new KernelMemoryBuilder()
-            .WithAzureOpenAITextGeneration(azureOpenAITextConfig)
-            .WithAzureOpenAITextEmbeddingGeneration(azureOpenAIEmbeddingConfig)
+            .WithOllamaTextEmbeddingGeneration(ollamaConfig)
+            .WithOllamaTextGeneration(ollamaConfig)
             .WithPostgresMemoryDb(postgresConfig)
             .WithSimpleFileStorage(SimpleFileStorageConfig.Persistent)
             .Build();
@@ -44,16 +42,16 @@ private static async Task Test1()
         var mem2 = new KernelMemoryBuilder()
             .WithPostgresMemoryDb(postgresConfig)
             .WithSimpleFileStorage(SimpleFileStorageConfig.Persistent)
-            .WithAzureOpenAITextGeneration(azureOpenAITextConfig)
-            .WithAzureOpenAITextEmbeddingGeneration(azureOpenAIEmbeddingConfig)
+            .WithOllamaTextEmbeddingGeneration(ollamaConfig)
+            .WithOllamaTextGeneration(ollamaConfig)
             .Build();
 
         // Concatenate our 'WithPostgresMemoryDb()' before and after KM builder extension methods from the core nuget
         var mem3 = new KernelMemoryBuilder()
             .WithSimpleFileStorage(SimpleFileStorageConfig.Persistent)
-            .WithAzureOpenAITextGeneration(azureOpenAITextConfig)
+            .WithOllamaTextEmbeddingGeneration(ollamaConfig)
+            .WithOllamaTextGeneration(ollamaConfig)
             .WithPostgresMemoryDb(postgresConfig)
-            .WithAzureOpenAITextEmbeddingGeneration(azureOpenAIEmbeddingConfig)
             .Build();
 
         await mem1.DeleteIndexAsync("index1");
@@ -92,22 +90,20 @@ private static async Task Test1()
     private static async Task Test2()
     {
         var postgresConfig = new PostgresConfig();
-        var azureOpenAIEmbeddingConfig = new AzureOpenAIConfig();
-        var azureOpenAITextConfig = new AzureOpenAIConfig();
+        var ollamaConfig = new OllamaConfig();
 
         new ConfigurationBuilder()
             .AddJsonFile("appsettings.json")
             .AddJsonFile("appsettings.development.json", optional: true)
             .AddJsonFile("appsettings.Development.json", optional: true)
             .Build()
             .BindSection("KernelMemory:Services:Postgres", postgresConfig)
-            .BindSection("KernelMemory:Services:AzureOpenAIEmbedding", azureOpenAIEmbeddingConfig)
-            .BindSection("KernelMemory:Services:AzureOpenAIText", azureOpenAITextConfig);
+            .BindSection("KernelMemory:Services:Ollama", ollamaConfig);
 
         var memory = new KernelMemoryBuilder()
             .WithPostgresMemoryDb(postgresConfig)
-            .WithAzureOpenAITextGeneration(azureOpenAITextConfig)
-            .WithAzureOpenAITextEmbeddingGeneration(azureOpenAIEmbeddingConfig)
+            .WithOllamaTextGeneration(ollamaConfig)
+            .WithOllamaTextEmbeddingGeneration(ollamaConfig)
             .WithSimpleFileStorage(new SimpleFileStorageConfig
             {
                 StorageType = FileSystemTypes.Disk,
@@ -140,8 +136,7 @@ private static async Task Test2()
     private static async Task Test3()
     {
         var postgresConfig = new PostgresConfig();
-        var azureOpenAIEmbeddingConfig = new AzureOpenAIConfig();
-        var azureOpenAITextConfig = new AzureOpenAIConfig();
+        var ollamaConfig = new OllamaConfig();
 
         // Note: using appsettings.custom-sql.json
         new ConfigurationBuilder()
@@ -151,13 +146,12 @@ private static async Task Test3()
             .AddJsonFile("appsettings.custom-sql.json")
             .Build()
             .BindSection("KernelMemory:Services:Postgres", postgresConfig)
-            .BindSection("KernelMemory:Services:AzureOpenAIEmbedding", azureOpenAIEmbeddingConfig)
-            .BindSection("KernelMemory:Services:AzureOpenAIText", azureOpenAITextConfig);
+            .BindSection("KernelMemory:Services:Ollama", ollamaConfig);
 
         var memory = new KernelMemoryBuilder()
             .WithPostgresMemoryDb(postgresConfig)
-            .WithAzureOpenAITextGeneration(azureOpenAITextConfig)
-            .WithAzureOpenAITextEmbeddingGeneration(azureOpenAIEmbeddingConfig)
+            .WithOllamaTextGeneration(ollamaConfig)
+            .WithOllamaTextEmbeddingGeneration(ollamaConfig)
             .WithSimpleFileStorage(new SimpleFileStorageConfig
             {
                 StorageType = FileSystemTypes.Disk,

extensions/Postgres/Postgres/Internals/PostgresDbClient.cs

@@ -59,6 +59,14 @@
 
         this._columnsListNoEmbeddings = $"{this._colId},{this._colTags},{this._colContent},{this._colPayload}";
         this._columnsListWithEmbeddings = $"{this._colId},{this._colTags},{this._colContent},{this._colPayload},{this._colEmbedding}";
+        this._columnsListHybrid = $"{this._colId},{this._colTags},{this._colContent},{this._colPayload},{this._colEmbedding}";
+        this._columnsListHybridCoalesce = $@"
+                                            COALESCE(semantic_search.{this._colId}, keyword_search.{this._colId}) AS {this._colId},
+                                            COALESCE(semantic_search.{this._colTags}, keyword_search.{this._colTags}) AS {this._colTags},
+                                            COALESCE(semantic_search.{this._colContent}, keyword_search.{this._colContent}) AS {this._colContent},
+                                            COALESCE(semantic_search.{this._colPayload}, keyword_search.{this._colPayload}) AS {this._colPayload},
+                                            COALESCE(semantic_search.{this._colEmbedding}, keyword_search.{this._colEmbedding}) AS {this._colEmbedding},
+                                         ";
 
         this._createTableSql = string.Empty;
         if (config.CreateTableSql?.Count > 0)
@@ -138,6 +146,8 @@
         CancellationToken cancellationToken = default)
     {
         var origInputTableName = tableName;
+        var indexTags = this.WithTableNamePrefix(tableName) + "_idx_tags";
+        var indexContent = this.WithTableNamePrefix(tableName) + "_idx_content";
         tableName = this.WithSchemaAndTableNamePrefix(tableName);
         this._log.LogTrace("Creating table: {0}", tableName);
 
@@ -175,7 +185,8 @@
                                 {this._colContent}   TEXT DEFAULT '' NOT NULL,
                                 {this._colPayload}   JSONB DEFAULT '{{}}'::JSONB NOT NULL
                             );
-                            CREATE INDEX IF NOT EXISTS idx_tags ON {tableName} USING GIN({this._colTags});
+                            CREATE INDEX IF NOT EXISTS ""{indexTags}"" ON {tableName} USING GIN({this._colTags});
+                            CREATE INDEX IF NOT EXISTS ""{indexContent}"" ON {tableName} USING GIN(to_tsvector('english',{this._colContent}));
                             COMMIT;
                         ";
 #pragma warning restore CA2100
@@ -388,23 +399,27 @@
     /// Get a list of records
     /// </summary>
     /// <param name="tableName">Table containing the records to fetch</param>
+    /// <param name="query">Prompt query. Only used in the case of hybrid search</param>
     /// <param name="target">Source vector to compare for similarity</param>
     /// <param name="minSimilarity">Minimum similarity threshold</param>
     /// <param name="filterSql">SQL filter to apply</param>
     /// <param name="sqlUserValues">List of user values passed with placeholders to avoid SQL injection</param>
     /// <param name="limit">Max number of records to retrieve</param>
     /// <param name="offset">Records to skip from the top</param>
     /// <param name="withEmbeddings">Whether to include embedding vectors</param>
+    /// <param name="useHybridSearch">Whether to use hybrid search or vector search</param>
     /// <param name="cancellationToken">Async task cancellation token</param>
     public async IAsyncEnumerable<(PostgresMemoryRecord record, double similarity)> GetSimilarAsync(
         string tableName,
+        string query,
         Vector target,
         double minSimilarity,
         string? filterSql = null,
         Dictionary<string, object>? sqlUserValues = null,
         int limit = 1,
         int offset = 0,
         bool withEmbeddings = false,
+        bool useHybridSearch = false,
         [EnumeratorCancellation] CancellationToken cancellationToken = default)
     {
         tableName = this.WithSchemaAndTableNamePrefix(tableName);
@@ -413,14 +428,19 @@
 
         // Column names
         string columns = withEmbeddings ? this._columnsListWithEmbeddings : this._columnsListNoEmbeddings;
+        string columnsHibrid = this._columnsListHybrid;
+        string columnsListHybridCoalesce = this._columnsListHybridCoalesce;
 
         // Filtering logic, including filter by similarity
+        //
         filterSql = filterSql?.Trim().Replace(PostgresSchema.PlaceholdersTags, this._colTags, StringComparison.Ordinal);
         if (string.IsNullOrWhiteSpace(filterSql))
         {
             filterSql = "TRUE";
         }
 
+		string filterSqlHybridText = filterSql;
+
         var maxDistance = 1 - minSimilarity;
         filterSql += $" AND {this._colEmbedding} <=> @embedding < @maxDistance";
 
@@ -440,16 +460,51 @@
 #pragma warning disable CA2100 // SQL reviewed
                     string colDistance = "__distance";
 
-                    // When using 1 - (embedding <=> target) the index is not being used, therefore we calculate
-                    // the similarity (1 - distance) later. Furthermore, colDistance can't be used in the WHERE clause.
-                    cmd.CommandText = @$"
-                        SELECT {columns}, {this._colEmbedding} <=> @embedding AS {colDistance}
-                        FROM {tableName}
-                        WHERE {filterSql}
-                        ORDER BY {colDistance} ASC
+                    if (useHybridSearch)
+                    {
+                        // When using 1 - (embedding <=> target) the index is not being used, therefore we calculate
+                        // the similarity (1 - distance) later. Furthermore, colDistance can't be used in the WHERE clause.
+                        cmd.CommandText = @$"
+                        WITH semantic_search AS (
+                            SELECT {columnsHibrid}, RANK () OVER (ORDER BY {this._colEmbedding} <=> @embedding) AS rank
+                            FROM {tableName}
+                            WHERE {filterSql}
+                            ORDER BY {this._colEmbedding} <=> @embedding
+                            LIMIT @limit
+                        ),
+                        keyword_search AS (
+                            SELECT {columnsHibrid}, RANK () OVER (ORDER BY ts_rank_cd(to_tsvector('english', {this._colContent}), query) DESC)
+                            FROM {tableName}, plainto_tsquery('english', @query) query
+                            WHERE  {filterSqlHybridText} AND to_tsvector('english', {this._colContent}) @@ query
+                            ORDER BY ts_rank_cd(to_tsvector('english', {this._colContent}), query) DESC
+                            LIMIT @limit
+                        )
+                        SELECT
+                            {columnsListHybridCoalesce}
+                            COALESCE(1.0 / (60 + semantic_search.rank), 0.0) +
+                            COALESCE(1.0 / (60 + keyword_search.rank), 0.0) AS {colDistance}
+                        FROM semantic_search
+                        FULL OUTER JOIN keyword_search ON semantic_search.{this._colId} = keyword_search.{this._colId}
+                        ORDER BY {colDistance} DESC
                         LIMIT @limit
                         OFFSET @offset
                     ";
+                        cmd.Parameters.AddWithValue("@query", query);
+                        cmd.Parameters.AddWithValue("@minSimilarity", minSimilarity);
+                    }
+                    else
+                    {
+                        // When using 1 - (embedding <=> target) the index is not being used, therefore we calculate
+                        // the similarity (1 - distance) later. Furthermore, colDistance can't be used in the WHERE clause.
+                        cmd.CommandText = @$"
+                            SELECT {columns}, {this._colEmbedding} <=> @embedding AS {colDistance}
+                            FROM {tableName}
+                            WHERE {filterSql}
+                            ORDER BY {colDistance} ASC
+                            LIMIT @limit
+                            OFFSET @offset
+                        ";
+                    }
 
                     cmd.Parameters.AddWithValue("@embedding", target);
                     cmd.Parameters.AddWithValue("@maxDistance", maxDistance);
@@ -692,6 +747,8 @@
     private readonly string _colPayload;
     private readonly string _columnsListNoEmbeddings;
     private readonly string _columnsListWithEmbeddings;
+    private readonly string _columnsListHybrid;
+    private readonly string _columnsListHybridCoalesce;
     private readonly bool _dbNamePresent;
 
     /// <summary>

extensions/Postgres/Postgres/PostgresConfig.cs

@@ -107,6 +107,12 @@ public class PostgresConfig
     /// </summary>
     public List<string> CreateTableSql { get; set; } = [];
 
+    /// <summary>
+    /// Important: when using hybrid search, relevance scores
+    /// are very different from when using just vector search.
+    /// </summary>
+    public bool UseHybridSearch { get; set; } = false;
+
     /// <summary>
     /// Create a new instance of the configuration
     /// </summary>

extensions/Postgres/Postgres/PostgresMemory.cs

@@ -28,6 +28,8 @@ public sealed class PostgresMemory : IMemoryDb, IDisposable, IAsyncDisposable
     private readonly ITextEmbeddingGenerator _embeddingGenerator;
     private readonly ILogger<PostgresMemory> _log;
 
+    private readonly bool _useHybridSearch;
+
     /// <summary>
     /// Create a new instance of Postgres KM connector
     /// </summary>
@@ -40,6 +42,7 @@ public PostgresMemory(
         ILoggerFactory? loggerFactory = null)
     {
         this._log = (loggerFactory ?? DefaultLogger.Factory).CreateLogger<PostgresMemory>();
+        this._useHybridSearch = config.UseHybridSearch;
 
         this._embeddingGenerator = embeddingGenerator;
         if (this._embeddingGenerator == null)
@@ -159,12 +162,14 @@ await this._db.UpsertAsync(
 
         var records = this._db.GetSimilarAsync(
             index,
+            query: text,
             target: new Vector(textEmbedding.Data),
             minSimilarity: minRelevance,
             filterSql: sql,
             sqlUserValues: unsafeSqlUserValues,
             limit: limit,
             withEmbeddings: withEmbeddings,
+            useHybridSearch: this._useHybridSearch,
             cancellationToken: cancellationToken).ConfigureAwait(false);
 
         await foreach ((PostgresMemoryRecord record, double similarity) result in records)

service/Service/appsettings.json

@@ -624,7 +624,10 @@
         "ConnectionString": "Host=localhost;Port=5432;Username=public;Password=;Database=public",
         // Mandatory prefix to add to the name of table managed by KM,
         // e.g. to exclude other tables in the same schema.
-        "TableNamePrefix": "km-"
+        "TableNamePrefix": "km-",
+        // Hybrid search is not enabled by default. Note that when using hybrid search
+        // relevance scores are different, usually lower, than when using just vector search
+        "UseHybridSearch": false,
       },
       "Qdrant": {
         // Qdrant endpoint