Improve postgres memory (#1794)

### Motivation and Context
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  2. What problem does it solve?
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Follow
#1735 (review)
advice to rename methods and separate responsibilities.

### Description
<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->
- Separate the responsibilities of PostgresMemoryStore and
PostgresDbClient.
- Add the real batch methods to PostgresDbClient.
- Save timestamp with `TIMESTAMP WITH TIME ZONE` type
- Stop creating index

### Contribution Checklist
<!-- Before submitting this PR, please make sure: -->
- [x] The code builds clean without any errors or warnings
- [x] The PR follows SK Contribution Guidelines
(https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
- [x] The code follows the .NET coding conventions
(https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions)
verified with `dotnet format`
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Dmytro Struk <13853051+dmytrostruk@users.noreply.github.com>

dotnet/samples/KernelSyntaxExamples/Example39_Postgres.cs

@@ -20,7 +20,7 @@ public static async Task RunAsync()
         dataSourceBuilder.UseVector();
         using NpgsqlDataSource dataSource = dataSourceBuilder.Build();
 
-        PostgresMemoryStore memoryStore = new(dataSource, vectorSize: 1536, schema: "public", numberOfLists: 100);
+        PostgresMemoryStore memoryStore = new(dataSource, vectorSize: 1536, schema: "public");
 
         IKernel kernel = Kernel.Builder
             .WithLogger(ConsoleLogger.Log)

dotnet/src/Connectors/Connectors.Memory.Pinecone/Model/IndexDefinition.cs

@@ -3,7 +3,6 @@
 using System.Net.Http;
 using System.Text;
 using System.Text.Json.Serialization;
-using Microsoft.SemanticKernel.Connectors.Memory.Pinecone.Http;
 
 namespace Microsoft.SemanticKernel.Connectors.Memory.Pinecone.Model;
 

dotnet/src/Connectors/Connectors.Memory.Postgres/IPostgresDbClient.cs

@@ -1,5 +1,6 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using System;
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
@@ -13,76 +14,95 @@ namespace Microsoft.SemanticKernel.Connectors.Memory.Postgres;
 public interface IPostgresDbClient
 {
     /// <summary>
-    /// Check if a collection exists.
+    /// Check if a table exists.
     /// </summary>
-    /// <param name="collectionName">The name assigned to a collection of entries.</param>
+    /// <param name="tableName">The name assigned to a table of entries.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns></returns>
-    Task<bool> DoesCollectionExistsAsync(string collectionName, CancellationToken cancellationToken = default);
+    Task<bool> DoesTableExistsAsync(string tableName, CancellationToken cancellationToken = default);
 
     /// <summary>
-    /// Create a collection.
+    /// Create a table.
     /// </summary>
-    /// <param name="collectionName">The name assigned to a collection of entries.</param>
+    /// <param name="tableName">The name assigned to a table of entries.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns></returns>
-    Task CreateCollectionAsync(string collectionName, CancellationToken cancellationToken = default);
+    Task CreateTableAsync(string tableName, CancellationToken cancellationToken = default);
 
     /// <summary>
-    /// Get all collections.
+    /// Get all tables.
     /// </summary>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
-    /// <returns></returns>
-    IAsyncEnumerable<string> GetCollectionsAsync(CancellationToken cancellationToken = default);
+    /// <returns>A group of tables.</returns>
+    IAsyncEnumerable<string> GetTablesAsync(CancellationToken cancellationToken = default);
 
     /// <summary>
-    /// Delete a collection.
+    /// Delete a table.
     /// </summary>
-    /// <param name="collectionName">The name assigned to a collection of entries.</param>
+    /// <param name="tableName">The name assigned to a table of entries.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns></returns>
-    Task DeleteCollectionAsync(string collectionName, CancellationToken cancellationToken = default);
+    Task DeleteTableAsync(string tableName, CancellationToken cancellationToken = default);
 
     /// <summary>
-    /// Upsert entry into a collection.
+    /// Upsert entry into a table.
     /// </summary>
-    /// <param name="collectionName">The name assigned to a collection of entries.</param>
+    /// <param name="tableName">The name assigned to a table of entries.</param>
     /// <param name="key">The key of the entry to upsert.</param>
     /// <param name="metadata">The metadata of the entry.</param>
     /// <param name="embedding">The embedding of the entry.</param>
-    /// <param name="timestamp">The timestamp of the entry</param>
+    /// <param name="timestamp">The timestamp of the entry. Its 'DateTimeKind' must be <see cref="DateTimeKind.Utc"/></param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns></returns>
-    Task UpsertAsync(string collectionName, string key, string? metadata, Vector? embedding, long? timestamp, CancellationToken cancellationToken = default);
+    Task UpsertAsync(string tableName, string key, string? metadata, Vector? embedding, DateTime? timestamp, CancellationToken cancellationToken = default);
 
     /// <summary>
     /// Gets the nearest matches to the <see cref="Vector"/>.
     /// </summary>
-    /// <param name="collectionName">The name assigned to a collection of entries.</param>
-    /// <param name="embeddingFilter">The <see cref="Vector"/> to compare the collection's embeddings with.</param>
+    /// <param name="tableName">The name assigned to a table of entries.</param>
+    /// <param name="embedding">The <see cref="Vector"/> to compare the table's embeddings with.</param>
     /// <param name="limit">The maximum number of similarity results to return.</param>
     /// <param name="minRelevanceScore">The minimum relevance threshold for returned results.</param>
     /// <param name="withEmbeddings">If true, the embeddings will be returned in the entries.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
-    /// <returns></returns>
-    IAsyncEnumerable<(PostgresMemoryEntry, double)> GetNearestMatchesAsync(string collectionName, Vector embeddingFilter, int limit, double minRelevanceScore = 0, bool withEmbeddings = false, CancellationToken cancellationToken = default);
+    /// <returns>An asynchronous stream of <see cref="PostgresMemoryEntry"/> objects that the nearest matches to the <see cref="Vector"/>.</returns>
+    IAsyncEnumerable<(PostgresMemoryEntry, double)> GetNearestMatchesAsync(string tableName, Vector embedding, int limit, double minRelevanceScore = 0, bool withEmbeddings = false, CancellationToken cancellationToken = default);
 
     /// <summary>
     /// Read a entry by its key.
     /// </summary>
-    /// <param name="collectionName">The name assigned to a collection of entries.</param>
+    /// <param name="tableName">The name assigned to a table of entries.</param>
     /// <param name="key">The key of the entry to read.</param>
-    /// <param name="withEmbeddings">If true, the embeddings will be returned in the entries.</param>
+    /// <param name="withEmbeddings">If true, the embeddings will be returned in the entry.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns></returns>
-    Task<PostgresMemoryEntry?> ReadAsync(string collectionName, string key, bool withEmbeddings = false, CancellationToken cancellationToken = default);
+    Task<PostgresMemoryEntry?> ReadAsync(string tableName, string key, bool withEmbeddings = false, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Read multiple entries by their keys.
+    /// </summary>
+    /// <param name="tableName">The name assigned to a table of entries.</param>
+    /// <param name="keys">The keys of the entries to read.</param>
+    /// <param name="withEmbeddings">If true, the embeddings will be returned in the entries.</param>
+    /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
+    /// <returns>An asynchronous stream of <see cref="PostgresMemoryEntry"/> objects that match the given keys.</returns>
+    IAsyncEnumerable<PostgresMemoryEntry> ReadBatchAsync(string tableName, IEnumerable<string> keys, bool withEmbeddings = false, CancellationToken cancellationToken = default);
 
     /// <summary>
     /// Delete a entry by its key.
     /// </summary>
-    /// <param name="collectionName">The name assigned to a collection of entries.</param>
+    /// <param name="tableName">The name assigned to a table of entries.</param>
     /// <param name="key">The key of the entry to delete.</param>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns></returns>
-    Task DeleteAsync(string collectionName, string key, CancellationToken cancellationToken = default);
+    Task DeleteAsync(string tableName, string key, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Delete multiple entries by their key.
+    /// </summary>
+    /// <param name="tableName">The name assigned to a table of entries.</param>
+    /// <param name="keys">The keys of the entries to delete.</param>
+    /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
+    /// <returns></returns>
+    Task DeleteBatchAsync(string tableName, IEnumerable<string> keys, CancellationToken cancellationToken = default);
 }