How Can I Resolve EF 6 Query Timeouts Caused by Parameter Sniffing?

EF 6 Parameter Sniffing and the "OPTION RECOMPILE" Hint

Your issue with EF 6 query timeouts, despite efficient SQL in SSMS, suggests parameter sniffing. To resolve this, consider the following:

Can EF Embed "OPTION RECOMPILE" Hint?

Yes, EF 6 allows for interception of SQL commands before execution. You can add the "OPTION RECOMPILE" hint by implementing an IDbCommandInterceptor. Here's an example implementation:

public class OptionRecompileHintDbCommandInterceptor : IDbCommandInterceptor
{
    public 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)";
        }
    }

    // Implementation of other interface methods...
}

To use this interceptor, simply add it to your application at the start:

DbInterception.Add(new OptionRecompileHintDbCommandInterceptor());

Further Considerations

• Ensure that table statistics are up-to-date, as they can affect parameter sniffing.
• Consider using WithCompileOptions(new QueryCompilationContext()) to enforce recompilation of the query.
• If the query is extremely complex, try optimizing it through manual tuning or using query hints.

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