What is the best way to detect Select n+1 problems if i am using linq to SQL, right now we are working on a project and it seem to be pretty slow to display some lists.
What is the best method to detect this?
Maybe this will help:
http://ayende.com/Blog/archive/2009/11/13/linq-to-sql-profiler-is-now-on-public-beta.aspx
http://weblogs.asp.net/scottgu/archive/2007/07/31/linq-to-sql-debug-visualizer.aspx
http://visualstudiogallery.msdn.microsoft.com/ru-ru/d5a64d5a-174a-4357-ad84-dbeeec030f23
Or you can use SQL Profiler and just check if queries are executed when you access individual list items.
This won't outright detect n+1 problems, but they're pretty easy to spot when you look at your generated SQL.
The DataContext.Log property takes a TextWriter that will output the generated SQL and some other diagnostic information. Here's an implementation that logs to the output. Linq to SQL DebuggerWriter. Here's the simple example of how to use the DebuggerWriter.
DataContext db = new DataContext();
#if DEBUG
db.Log = new DebuggerWriter();
#endif
Related
One of our contractors implemented a repository pattern with code first approach. We use Service Locator as DI pattern. what we do when we retrieve data from DB, we pass interface to GetQueryable function and get the data. However, I see serious performance issues on our application. I implemented MiniProfiler and MiniProfiler.EF to see where the bottleneck is.
We have a case table which has quite a few fields(around 25) and some of those fields are associated to other tables as one to one and one to many(only one field has many relation to other table). when I try to see the case detail, it runs around 400 SQL queries and SQL takes around 40 percent of the load time as far as the miniprofiler concerned. Here our GetQueryable and Find methods
public IQueryable<T> GetQueryable<T>(params string[] includes)
{
Type type = _impls.Value[typeof (T).Name].GetType();
DbSet dbSet = Db.Set(type);
foreach (var include in includes)
{
dbSet.Include(include);
}
return ((IQueryable<T>) dbSet);
}
I added included to this method to attach other related tables, but it did not make any difference. and here is the Find Method
public T Find<T>(long? id)
{
Type type = _impls.Value[typeof(T).Name].GetType();
return (T) Db.Set(type).Find(id);
}
I pretty much tried to apply all the performance improvements, but the number of the SQL queries has not gone down. I tried to disable lazy loading, but it caused many problems in other parts of the application.
Just some additional information, in case table, there are 70000 rows and in out dialogs table, there are 500000 rows. Case and Dialog are associates as one-to-many. and each case has 20-40 dialog entries.
My questions are;
Why does include not make any difference when I use?
Is there any other way to crop number of the queries run?
Do you think the implementation is the problem?
Thanks
Include returns a new IQueryable and does not modify the source query. In addition you can use the generic version of Set which simplifies the code a bit:
public IQueryable<T> GetQueryable<T>(params string[] includes)
{
IQueryable<T> query = Db.Set<T>();
foreach (var include in includes)
{
query = query.Include(include);
}
return query;
}
Step 1: Fire your contractor. Seriously. Like right now. That is some awful code. Not only did they miss something as simple and basic as using the generic version of Set, but they've successfully only made working with Entity Framework more complex, because all the repository does is proxy Entity Framework methods with its own unique and bastardized API.
That said, there's really not enough here to diagnose what your problem is. The use of Include may give you larger queries, but it should actually serve to reduce the overall number of queries issued. It's possible, you're just not using includes where you should be.
Now, the fact that you "tried to disable lazy loading, but it caused many problems in other parts of the application", means that you're relying too heavily on lazy-loading. Basically, you're loading in stuff you don't even know about, which is the antithesis of optimization. Ironically, you'd actually be best served by going ahead and disabling lazy-loading, and then tracking down where your code fails because of that. If you want to actually lazy-load that thing, you can use .Load (see: Explicit Loading). But, if you want to eager-load to reduce queries, then you know what includes you need to add.
I just hooked up MiniProfiler to my MVC3 project. I am using EF4.0 and generating POCO classes for my entities.
If it matters, these generated ObjectContexts use ObjectSet<>. I am also using NInject for IoC on the contexts. (I had these in RequestScope, but I changed them to TransientScope to rule that issue out).
All of the profiling that I am seeing is showing "ExecuteStoreCommands" as the query.
Any ideas as to why "ExecuteStoreCommands" would be showing up instead of the SQL? I see real sql in SQL Profiler that looks like this:
exec sp_executesql N'SELECT
[Project2].[OrderID] AS [OrderID],
...
Am I having trouble because I'm not on EF4.1/4.2/4.3? Is it because I didn't use CodeFirst? Is it the POCOs?
It looks like I'm having trouble with the MiniProfiler library. The serialization of the SqlTiming object (via FromJSON) saves the FormattedCommandString which only has a get method. On deserialization, this meant that the CommandString and FormattedCommandString were both null.
The quick (hacky) fix before Deserialization was:
profilerString = profilerString.Replace("FormattedCommandString", "CommandString");
var profiler = MiniProfiler.FromJson(profilerString);
There often are times when I would like to see what SQL is being generated by EF. For instance I query an object, modify it and save it back:
var context = new EntityModel();
var MyObj = context.FooTable.First(o => o.id = SearchId);
MyObj.Property = SomeValue;
context.SaveChanges();
I get some silly error that I may be able to troubleshoot if I could see the SQL. I am far from a EF expert and it would help me learn too.
Update: I think what I really want to know is: In auto-tracking EF objects as shown above, how do I get at the ObjectContext/ObjectQuery to use ToTraceString() to see what was executed in SaveChanges()?
I use the free SQL Express Profiler
It sounds like pretty easy task but it is not because ADO.NET team somehow forgot to include such basich functionality. Check EF Tracing provider. That is something which can help you log SQL commands. Otherwise go with SQL Profiler and learn how to use filters when establishing new trace.
the EF Profiler is a great tool for this - its not free though :(
is there an possibility to call the Math.Sin()-function in a Linq To Entites (Entity Framework 4) -Query?
I've read, that the current Entity Framework 4 doesn't implement this function.
Maybe there's a workaround to this solve problem?
(I don't want to invite all entries in the memory.)
Thanks and best regards
Several functions that (usually) have obvious SQL counterparts, like Math.Sin can't be used directly in Entity Framework queries. Presumably this is because they can't be reliably translated to different SQL implementations. A ton of MSSQL-specific functions are, however, exposed as static methods in the class System.Data.Objects.SqlClient.SqlFunctions. They throw exceptions if you call them directly, but are translated into the proper SQL if used in a LINQ query.
See this blog post about the magic that's happening under the covers (namely the EdmFunction attribute).
It is certainly possible to use such function starting with EF4. In EF4, EF team introduced SqlServer functions that can be consumed in linq. You should alway consider using canonical functions cuz they are database agnostic and every vendor should convert those functions to store specific equivalent. However when such functions are not available, you can resort to SqlServer namespace (ESQL) or SqlFunctions for linq
from l in db.Locations
select SqlServer.Sin(l.Latitude) + SqlServer.power(l.Longitutde)
I cover several of these options in my functions chapter in my book. Specifically you can look at 11-10 recipe Calling database function in esql
11-11 Calling Database Function in LINQ
Unfortunately it's impossible to call Math.Sin in a LinqToEntities query (or Entity SQL query).
The only way to accomplish this without resorting to retrieving all objects first, is to write a SQL query that does what you want and call it via ObjectContext.ExecuteStoreQuery. This isn't as bad as it sounds because you can still get back typed results.
EDIT: After reading the other answers, it appears that it is possible to call these types of functions (SqlFunctions contains 44 functions with various overloads). I leave my original answer as is because it's another way of achieving the same result.
I started working with linq to SQL several weeks ago. I got really tired of working with SQL server directly through the SQL queries (sqldatareader, sqlcommand and all this good stuff).
After hearing about linq to SQL and mvc I quickly moved all my projects to these technologies. I expected linq to SQL work slower but it suprisongly turned out to be pretty fast, primarily because I always forgot to close my connections when using datareaders. Now I don't have to worry about it.
But there's one problem that really bothers me. There's one page that's requested thousands of times a day. The system gets data in the beginning, works with it and updates it. Primarily the updates are ++ # -- (increase and decrease values). I used to do it like this
UPDATE table SET value=value+1 WHERE ID=#I'd
It worked with no problems obviously. But with linq to SQL the data is taken in the beginning, moved to the class, changed and then saved.
Stats.registeredusers++;
Db.submitchanges();
Let's say there were 100 000 users. Linq will say "let it be 100 001" instead of "let it be increased by 1".
But if there value of users has already been increased (that happens in my site all the time) then linq will be like oops, this value is already 100 001. Whatever I'll throw an exception"
You can change this behavior so that it won't throw an exception but it still will not set the value to 100 002.
Like I said, it happened with me all the time. The stas value was increased twice a second on average. I simply had to rewrite this chunk of code with classic ado net.
So my question is how can you solve the problem with linq
For these types of "write-only queries" I usually use a Stored Procedure. You can drag the stored procedure into the designer and execute it through the Linq to SQL DataContext class (it will be added as a method).
Sorry for the trite answer but it really is that simple; no need to to finagle with raw ADO.NET SqlCommand objects and the like, just import the SP and you're done. Or, if you want to go really ad-hoc, use the ExecuteCommand method, as in:
context.ExecuteCommand("UPDATE table SET value = value + 1 WHERE ID = {0}", id);
(But don't overuse this, it can get difficult to maintain since the logic is no longer contained in your DataContext instance. And before anybody jumps on this claiming it to be a SQL injection vulnerability, please note that ExecuteCommand/ExecuteQuery are smart methods that turn this into a parameterized statement/query.)
Linq to Sql supports "optimistic" concurrency out of the box. If you need tighter control, you can add a Timestamp column to your table, and Linq to Sql will use that timestamp to tighten the concurrency.
http://mtaulty.com/CommunityServer/blogs/mike_taultys_blog/archive/2008/07/01/10557.aspx
However, as Morten points out in the comments below, this solution is not going to perform well. Of course, you can always use ADO.NET to update the value, just like you were doing before; that won't adversely affect the operation of your Linq queries at all.
You could turn off concurrency on that property by changing the UpdateCheck value:
http://msdn.microsoft.com/en-us/library/bb399394(v=VS.90).aspx
Messy if your using generated code and the designer but I think this is the only way to do this.