Entity Framework Why First Query is slow?

public class MyDbConfiguration : DbConfiguration
{
    public MyDbConfiguration() : base()
    {
        var path = Path.GetDirectoryName(this.GetType().Assembly.Location);
        SetModelStore(new DefaultDbModelStore(path));
    }
}

public class MyContextConfiguration : DbConfiguration
{
    public MyContextConfiguration()
    {
        MyDbModelStore cachedDbModelStore = new MyDbModelStore(MyContext.EfCacheDirPath);
        IDbDependencyResolver dependencyResolver = new SingletonDependencyResolver<DbModelStore>(cachedDbModelStore);
        AddDependencyResolver(dependencyResolver);
    }

    private class MyDbModelStore : DefaultDbModelStore
    {
        public MyDbModelStore(string location)
            : base(location)
        {}

        public override DbCompiledModel TryLoad(Type contextType)
        {
            string path = GetFilePath(contextType);
            if(File.Exists(path))
            {
                DateTime lastWriteTime = File.GetLastWriteTimeUtc(path);
                DateTime lastWriteTimeDomainAssembly = File.GetLastWriteTimeUtc(typeof(MyDomain.SomeTypeInOurDomain).Assembly.Location);
                if (lastWriteTimeDomainAssembly > lastWriteTime)
                {
                    File.Delete(path);
                    Tracers.EntityFramework.TraceInformation("Cached db model obsolete. Re-creating cached db model edmx.");
                }
            }
            else
            {
                Tracers.EntityFramework.TraceInformation("No cached db model found. Creating cached db model edmx.");
            }

            return base.TryLoad(contextType);
        }
    }
}