Add support for specifying non-clustered index sort direction

README.md

@@ -110,6 +110,7 @@ columnOpts.Store.Add(StandardColumn.LogEvent);
 columnOpts.LogEvent.DataLength = 2048;
 columnOpts.PrimaryKey = columnOpts.TimeStamp;
 columnOpts.TimeStamp.NonClusteredIndex = true;
+columnOpts.TimeStamp.NonClusteredIndexDirection = SqlIndexDirection.Desc;
 
 var log = new LoggerConfiguration()
     .WriteTo.MSSqlServer(
@@ -349,6 +350,7 @@ Each Standard Column in the `ColumnOptions.Store` list and any custom columns yo
 * `AllowNull`
 * `DataLength`
 * `NonClusteredIndex`
+* `NonClusteredIndexDirection`
 
 ### ColumnName
 
@@ -412,9 +414,20 @@ Supported SQL column data types that use this property:
 
 Any individual column can be defined as a non-clustered index, including the table primary key. Use this with caution, indexing carries a relatively high write-throughput penalty. One way to mitigate this is to keep non-clustered indexes offline and use batch reindexing on a scheduled basis.
 
+### NonClusteredIndexDirection
+
+Specifies the sort direction (`ASC` or `DESC`) for a non-clustered index on the SQL column.
+The default value is `ASC`.
+
+It is especially useful for the timestamp column,
+where choosing the correct sort direction can optimize query performance for workloads that typically scan
+recent data first.
+
+This only has effect if `NonClusteredIndex` is `true`.
+
 ## Standard Columns
 
-By default (and consistent with the SQL DDL to create a table shown earlier) these columns are included in a new `ColumnOptions.Store` list:
+By default (and consistent with the SQL DDL to create a table shown earlier), these columns are included in a new `ColumnOptions.Store` list:
 
  - `StandardColumn.Id`
  - `StandardColumn.Message`

src/Serilog.Sinks.MSSqlServer/Sinks/MSSqlServer/Platform/SqlCreateTableWriter.cs

@@ -54,7 +54,7 @@ public string GetSql()
 
                     // collect non-PK indexes for separate output after the table DDL
                     if (common != null && common.NonClusteredIndex && common != _columnOptions.PrimaryKey)
-                        ix.AppendLine(Invariant($"CREATE NONCLUSTERED INDEX [IX{indexCount++}_{_tableName}] ON [{_schemaName}].[{_tableName}] ([{common.ColumnName}]);"));
+                        ix.AppendLine(Invariant($"CREATE NONCLUSTERED INDEX [IX{indexCount++}_{_tableName}] ON [{_schemaName}].[{_tableName}] ([{common.ColumnName}] {common.NonClusteredIndexDirection});"));
                 }
             }
 

src/Serilog.Sinks.MSSqlServer/Sinks/MSSqlServer/SqlColumn.cs

@@ -100,6 +100,12 @@ public SqlDbType DataType
         /// </summary>
         public bool NonClusteredIndex { get; set; }
 
+        /// <summary>
+        /// Specifies the sort direction for a non-clustered index on the SQL column.
+        /// The default value is <see cref="SqlIndexDirection.Asc"/>. This property is only used when auto-creating a log table.
+        /// </summary>
+        public SqlIndexDirection NonClusteredIndexDirection { get; set; }
+
         /// <summary>
         /// The name of the Serilog property to use as the value when filling the DataTable.
         /// If not specified, the ColumnName and PropertyName are the same.

src/Serilog.Sinks.MSSqlServer/Sinks/MSSqlServer/SqlIndexDirection.cs

@@ -0,0 +1,18 @@
+namespace Serilog.Sinks.MSSqlServer
+{
+    /// <summary>
+    /// Defines the sort order for an SQL index.
+    /// </summary>
+    public enum SqlIndexDirection
+    {
+        /// <summary>
+        /// Represents the ascending direction for SQL indexing.
+        /// </summary>
+        Asc,
+
+        /// <summary>
+        /// Represents the descending direction for SQL indexing.
+        /// </summary>
+        Desc
+    }
+}