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POLinq to Sql and T-SQL Performance Discrepancy
 

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  1. POLinq to Sql and T-SQL Performance Discrepancy
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    <p>I have an MVC web site the presents a paged list of data records from a SQL Server database. The UI allows the user to filter the returned data on a number of different criteria, e.g. email address. Here is a snippet of code:</p> <pre><code>Stopwatch stopwatch = new Stopwatch(); var temp = SubscriberDB .GetSubscribers(model.Filter, model.PagingInfo); // Inspect SQL expression here stopwatch.Start(); model.Subscribers = temp.ToList(); stopwatch.Stop(); // 9 seconds plus compared to &lt; 1 second in Query Analyzer </code></pre> <p>When this code is run, the StopWatch shows an execution time of around 9 seconds. If I capture the generated SQL expression (just before it is evaluated with the .ToList() method) and cut'n'paste that as a query into SQL Server Management Studio, the execution times drops to less than 1 second. For reference here is the generated SQL expression:</p> <pre><code>SELECT [t2].[SubscriberId], [t2].[Email], [t3].[Reference] AS [DataSet], [t4].[Reference] AS [DataSource], [t2].[Created] FROM ( SELECT [t1].[SubscriberId], [t1].[SubscriberDataSetId], [t1].[SubscriberDataSourceId], [t1].[Email], [t1].[Created], [t1].[ROW_NUMBER] FROM ( SELECT ROW_NUMBER() OVER (ORDER BY [t0].[Email], [t0].[SubscriberDataSetId]) AS [ROW_NUMBER], [t0].[SubscriberId], [t0].[SubscriberDataSetId], [t0].[SubscriberDataSourceId], [t0].[Email], [t0].[Created] FROM [dbo].[inbox_Subscriber] AS [t0] WHERE [t0].[Email] LIKE '%_EMAIL_ADDRESS_%' ) AS [t1] WHERE [t1].[ROW_NUMBER] BETWEEN 0 + 1 AND 0 + 20 ) AS [t2] INNER JOIN [dbo].[inbox_SubscriberDataSet] AS [t3] ON [t3].[SubscriberDataSetId] = [t2].[SubscriberDataSetId] INNER JOIN [dbo].[inbox_SubscriberDataSource] AS [t4] ON [t4].[SubscriberDataSourceId] = [t2].[SubscriberDataSourceId] ORDER BY [t2].[ROW_NUMBER] </code></pre> <p>If I remove the email filter clause, then the controller's StopWatch returns a similar response time to the SQL Management Studio query, less than 1 second - so I am assuming that the basic interface to SQL plumbing is working correctly and that the problem lies with the evaluation of the Linq expression. I should also mention that this is quite a large database with upwards of 1M rows in the subscriber table.</p> <p>Can anyone throw any light on why there should be such a high (x10) performance differential and what, if anything can be done to address this?</p>
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    1. UStereško
    1. USNeilski
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      1. POLinq to Sql and T-SQL Performance Discrepancy
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    1. COThe common reasons for this are: parameter sniffing and differing SET options (ansi_nulls, ...). Try searching for them.
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      1. POLinq to Sql and T-SQL Performance Discrepancy
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    2. COIf you're running a non-express version of SQL server, fire up SQL Profiler and see if that's the only query that's going over. It might also give you a bit more insight into where the time is being spent.
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      1. POLinq to Sql and T-SQL Performance Discrepancy
      1. USRichard
    3. CO@Neilski - Can you show your GetSubscribers method?
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      1. POLinq to Sql and T-SQL Performance Discrepancy
      1. USErik Funkenbusch
 

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