How Can I Avoid Parameter Sniffing in EF 6 Dynamic Queries?

Parameter Sniffing in EF 6

When dealing with large dynamic queries in Entity Framework 6 (EF 6), it's possible to encounter performance issues due to parameter sniffing. This occurs when EF 6 caches the execution plan of a query based on the initial parameters passed, resulting in inefficient execution when the parameters change.

One solution to address parameter sniffing is to embed options such as "OPTION RECOMPILE" into the SQL command. This hints the database to recompile the execution plan every time the query is executed. However, EF 6 does not natively support adding such options.

Solution: EF Interception Feature

EF 6 provides an interception feature that allows you to manipulate its internal SQL commands before they are executed. This enables you to embed options like "OPTION RECOMPILE" dynamically.

To utilize this feature, you can create a custom IDbCommandInterceptor class. For example:

public class OptionRecompileHintDbCommandInterceptor : IDbCommandInterceptor
{
    // Add "OPTION RECOMPILE" hint to SQL commands before execution
    public void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
        addQueryHint(command);
    }

    private static void addQueryHint(IDbCommand command)
    {
        if (command.CommandType != CommandType.Text || !(command is SqlCommand))
            return;

        if (command.CommandText.StartsWith("select", StringComparison.OrdinalIgnoreCase) && !command.CommandText.Contains("option(recompile)"))
        {
            command.CommandText = command.CommandText + " option(recompile)";
        }
    }
}

To use this interceptor, simply add the following line at the start of your application:

DbInterception.Add(new OptionRecompileHintDbCommandInterceptor());

By implementing this solution, you can effectively avoid parameter sniffing and improve the performance of your dynamic queries in EF 6.

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