Finding slow queries with Entity Framework Interceptors

SlowQueryInterceptor.cs

using Microsoft.EntityFrameworkCore.Diagnostics;
using System.Data.Common;

namespace EntityFrameworkExamples;

public class SlowQueryInterceptor(ILogger<SlowQueryInterceptor> logger) : DbCommandInterceptor
{
    private const int _slowQueryThresholdInMilliseconds = 5; //from config

    public override DbDataReader ReaderExecuted(
        DbCommand command,
        CommandExecutedEventData eventData,
        DbDataReader result)
    {
        if (eventData.CommandSource == CommandSource.LinqQuery && eventData.Duration.TotalMilliseconds > _slowQueryThresholdInMilliseconds)
        {
            LogSlowQuery(command, eventData);
        }

        return base.ReaderExecuted(command, eventData, result);
    }

    public override ValueTask<DbDataReader> ReaderExecutedAsync(
        DbCommand command, 
        CommandExecutedEventData eventData, 
        DbDataReader result, 
        CancellationToken cancellationToken = default)
    {
        if (eventData.CommandSource == CommandSource.LinqQuery && eventData.Duration.TotalMilliseconds > _slowQueryThresholdInMilliseconds)
        {
            LogSlowQuery(command, eventData);
        }

        return base.ReaderExecutedAsync(command, eventData, result, cancellationToken);
    }

    private void LogSlowQuery(DbCommand command, CommandExecutedEventData eventData)
    {
        logger.LogWarning("Slow query detected : ({Duration} ms): {CommandText}",
            eventData.Duration.TotalMilliseconds, command.CommandText);
    }
}