How Can EF 6 Interception Solve Persistent Query Timeouts Caused by Parameter Sniffing?

EF 6 Parameter Sniffing Solution: Overcoming Query Timeout

Despite the efficiency of the SQL generated by your LINQ to Entities query, its execution through EF 6 incurs a persistent query timeout. This is likely due to parameter sniffing, a performance optimization technique used by the database engine. But you can't simply add an "OPTION RECOMPILE" command directly to your EF query.

Solution: Utilize EF Interception

EF 6 offers an interception feature that allows you to manipulate SQL commands before they execute on the database. By implementing a custom DbCommandInterceptor, you can add query hints, including "OPTION RECOMPILE," to the internal commands.

Here's the implementation of such an interceptor:

public class OptionRecompileHintDbCommandInterceptor : IDbCommandInterceptor
{
    public void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
        addQueryHint(command);
    }

    public void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<object> 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) &amp;&amp; !command.CommandText.Contains("option(recompile)"))
        {
            command.CommandText = command.CommandText + " option(recompile)";
        }
    }
}

To use this interceptor, simply add the following line to the beginning of your application:

DbInterception.Add(new OptionRecompileHintDbCommandInterceptor());

This will ensure that all EF-generated SQL commands have the "OPTION RECOMPILE" hint appended to them, preventing parameter sniffing and improving query performance.

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