increase speed of mysql when searching posts

modules/RichSiteSummary/Data/Post.cs

@@ -68,7 +68,7 @@ public class Post : RepresentableEntity
     /// The URI where this post is located in web.
     /// </summary>
     [Required]
-    [MaxLength(256)]
+    [MaxLength(1024)]
     public string Url { get; set; }
         
     /// <summary>
@@ -83,6 +83,13 @@ public class Post : RepresentableEntity
     [Required]
     public DateTime ReceivedAt { get; set; }
 
+    /// <summary>
+    /// 
+    /// </summary>
+    [Required]
+    [MaxLength(64)]
+    public string UrlHash { get; set; }
+
     public Post()
     {
         PostId = new Guid();