Large performance difference with EF6 join vs EF7 include

Windows 10, VS 2015, IIS Express, SQL Server Express 2014, EF 7.0.0-beta7, ASP.NET 6.0.0-beta7

I am seeing a large performance difference for a simple join in EF7 beta7 vs EF6. Using these models:

public class Blog
{
        public int BlogId { get; set; }

        [StringLength(100)]
        public String Name { get; set; }

        public DateTime DateStarted { get; set; }

        public String AuthorName { get; set; }

        public ICollection<Post> Posts { get; set; }
}

 public class Post
 {
        public int PostId { get; set; }

        public int BlogId { get; set; }

        public Blog Blog { get; set; }

        public DateTime DatePosted { get; set; }

        public String PostHtml { get; set; }
  }

Join code for EF6:

session.All<Post>().Join(session.All<Blog>(), b => b.BlogId, p => p.BlogId,
                (post, blog) => new TestModel {
                    Post = post,
                    Blog = blog
                }).ToList();

Which generates SQL:

SELECT 
[Extent1].[PostId] AS [PostId], 
[Extent1].[BlogId] AS [BlogId], 
[Extent1].[DatePosted] AS [DatePosted], 
[Extent1].[PostHtml] AS [PostHtml], 
[Extent2].[BlogId] AS [BlogId1], 
[Extent2].[AuthorName] AS [AuthorName], 
[Extent2].[DateStarted] AS [DateStarted], 
[Extent2].[Name] AS [Name]
FROM  [dbo].[Post] AS [Extent1]
INNER JOIN [dbo].[Blog] AS [Extent2] ON [Extent1].[BlogId] = [Extent2].[BlogId]

vs. EF7 join code:

_dbContext.Posts.Include(b => b.Blog).ToList();

Which generates SQL:

SELECT [b].[PostId], [b].[BlogId], [b].[DatePosted], [b].[PostHtml], [b0].[BlogId], [b0].[AuthorName], [b0].[DateStarted], [b0].[Name]
FROM [Post] AS [b]
INNER JOIN [Blog] AS [b0] ON [b].[BlogId] = [b0].[BlogId]

Both have similar execution plans, and with test data of 100 blogs and 100 posts per blog, run in a fraction of a second from SQL Server Management Studio. The EF6 query also runs in a fraction of a second. However, the EF7 query takes several seconds and causes IIS to garbage collect a number of times while it is running.

Here is the SQL Server Profiler output. The EF6 query is first, followed by the EF7 one:

Obviously this example is contrived, joining from many to few, but the actual code we have requires a similar join - starting from a cross-reference table and .Includeing to multiple source tables, where we are also seeing this performance issue.

[ahmad-moussawi]

(y) I think Important note like this, should be mentioned in the docs

[jparish9]

👍 This is for a web API so most of the queries returning a large result set are read-only. Thanks for the heads-up.