Add description field to metadata indexing for faster access

src/microsoft-update-partition/Metadata/UpdateBase.cs

@@ -164,18 +164,29 @@ public string Description
         {
             get
             {
-                if (_MetadataLoaded)
+                if (_DescriptionLoaded)
                 {
                     return _Description;
                 }
-                else
-                {
-                    LoadNonIndexedMetadataBase();
-                    return _Description;
-                }
-            }
+				else if (_FastLookupSource != null)
+				{
+					_FastLookupSource.TrySimpleKeyLookup<string>(_Id, Storage.Index.AvailableIndexes.DescriptionsIndexName, out string description);
+					return description;
+				}
+				else if (_MetadataSource != null)
+				{
+					LoadNonIndexedMetadataBase();
+					_DescriptionLoaded = true;
+					return _Description;
+				}
+				else
+				{
+					return null;
+				}
+			}
         }
-        private string _Description = null;
+		private bool _DescriptionLoaded;
+		private string _Description = null;
 
         /// <summary>
         /// Gets the list of files (content) for update
@@ -464,6 +475,7 @@ internal MicrosoftUpdatePackage(MicrosoftUpdatePackageIdentity id, XPathNavigato
             _TitleLoaded = true;
 
             _Description = UpdateParser.GetDescription(metadataNavigator, namespaceManager);
+            _DescriptionLoaded = true;
             _MetadataLoaded = true;
 
             _Prerequisites = PrerequisiteParser.FromXml(metadataNavigator, namespaceManager);

src/microsoft-update-partition/PackageGraph/Partitions/PartitionRegistration.cs

@@ -20,7 +20,7 @@ class PartitionRegistration
                     {
                         Factory = null,
                         HasExternalContentFileMetadata = false,
-                        Indexes = new List<IndexDefinition>() { TitlesIndex.TitlesIndexDefinition },
+                        Indexes = new List<IndexDefinition>() { TitlesIndex.TitlesIndexDefinition, DescriptionsIndex.DescriptionsIndexDefinition },
                         HandlesIdentities = false,
                     }
                 },

src/microsoft-update-partition/PackageGraph/Storage/Index/DescriptionsIndex.cs

@@ -0,0 +1,33 @@
+using Microsoft.PackageGraph.ObjectModel;
+
+namespace Microsoft.PackageGraph.Storage.Index
+{
+	class DescriptionsIndex : SimpleIndex<int, string>, ISimpleMetadataIndex<int, string>
+	{
+		internal static readonly IndexDefinition DescriptionsIndexDefinition =
+			new()
+			{
+				Name = AvailableIndexes.DescriptionsIndexName,
+				PartitionName = null,
+				Version = DescriptionsIndex.CurrentVersion,
+				Factory = new InternalIndexFactory(),
+				Tag = "stream"
+			};
+
+		public override IndexDefinition Definition => DescriptionsIndexDefinition;
+
+		public DescriptionsIndex(IIndexContainer container) : base(container, AvailableIndexes.TitlesIndexName)
+		{
+		}
+
+		public override void IndexPackage(IPackage package, int packageIndex)
+		{
+			Add(packageIndex, package.Description);
+		}
+
+		public new bool TryGet(int packageIndex, out string description)
+		{
+			return base.TryGet(packageIndex, out description);
+		}
+	}
+}

src/microsoft-update-partition/PackageGraph/Storage/Index/IndexTypes.cs

@@ -8,6 +8,7 @@ namespace Microsoft.PackageGraph.Storage.Index
     abstract class AvailableIndexes
     {
         public const string TitlesIndexName = "titles";
+        public const string DescriptionsIndexName = "descriptions";
     }
 
     class InternalIndexFactory : IIndexFactory
@@ -17,6 +18,7 @@ public IIndex CreateIndex(IndexDefinition definition, IIndexContainer container)
             return definition.Name switch
             {
                 AvailableIndexes.TitlesIndexName => new TitlesIndex(container),
+                AvailableIndexes.DescriptionsIndexName => new DescriptionsIndex(container),
                 _ => throw new NotImplementedException(),
             };
         }