Opening Up Query Batching
I have ranted before about the annoying trend from Microsoft, to weld the hood shut in most of the interesting places. One particulary painful piece is the command batching implementation in .Net 2.0 for SQL Server. The is extremely annoying mainly because the implementation benefits are going for those who are going to be using DataSets (ahem, not me), but are not avialable to anyone outside of Microsoft. (See topic: OR/M, NHibernate, etc).
Today, I have decided to actually check what the performance difference are all about. In order to do this, I opened the (wonderful, amazing) Reflector and started digging. To my surprise, I found that the Batching implementation seems to be centralized around a single class, System.Data.SqlClient.SqlCommandSet (which is internal, of course, to prevent it from being, you know, useful).
Since the class, and all its methods, are internal to System.Data, I had to use Reflection to pry them out into the open. I noticed that the cost of reflection was fairly high, so I converted the test to use delegates, which significantly imporved perfromance. The query I run was a very simple query:
INSERTINTO [Test].[dbo].[Blogs] ([blog_name]) VALUES (@name)
With the @name = 'foo' as the parameter value. The table is simple Id (identity), Blog_Name (nvarchar(50))
Note: Before each test, I truncated the table, to make sure it is not the additional data that is causing any slowdown.
The X axis is the number of inserts made, the Y axis is the number of ticks that the operation took. As you can see, there is quite a performance difference, even for small batch sizes. There is a significant difference between batching and not batching, and that reflection / delegates calls are not a big cost in this scenario.
Here is the cost of a smaller batch:
This shows a significant improvement even for a more real-world loads, even when we use Reflection.
I just may take advantage of this to implement a BatchingBatcher for NHibernate, it looks like it can make a good benefit for perfromance. Although this will probably not affect SELECT performance, which is usually a bigger issue.
You can get the code here: BatchingPerfTest.txt