Question

I have currently in a table about 90k rows. And it’s will grow up about 1kk ~ 5kk before i execute a clean up and put all rows in a “historical table”. So, when i run this following query (MyEntities is a ObjectSet):

MyEntities.Skip(amount * page).Take(amount).ToList();

This query takes about 1.2s… but when i run this following query with OrderBy and ThenBy:

MyEntities.OrderBy(b => b.Day).ThenBy(b => b.InitialHour).Skip(amount * page).Take(amount).ToList();

This query takes about 5.7s. There is a way to optimize the second query?

Answer 1

A few suggestions:

• Check that it really is happening in the database (instead of fetching all entities, then sorting)
• Make sure that both Day and InitialHour are indexed.
• Check the generated SQL isn’t doing anything crazy (check the query plan)

EDIT: Okay, so it looks like MyEntities is actually declared as IEnumerable<MyEntity>, which means everything will be done in-process… all your LINQ calls will be via Enumerable.Select etc, rather than Queryable.Select etc. Just change the declared type of MyEntities to IQueryable<MyEntity> and watch it fly…