DataTable Select vs List<T> LINQ Performance

Question

I have an app that does an SQL and loads a set of data into a datatable. As part of the processing there are 6 or 7 DataTable.Select() to filter some data. Each item that needs processing takes 300ms. There are 5000 items to process so takes 25 mins. This is unacceptable.

Would creating POCO's and loading them into a List and then using LINQ to query the list be quicker than using DataTable.Select?

Thanks

UPDATE: I have delved in a bit more and there are 2 datatables each with around 15000 records. The 2 queries used to populate the datatables take a second each. It then takes 25mins to loop over 5000 items in a Dictionary's values property and do 5 DataTable.Select's

eg/

foreach (OutputRecord Mailpiece in DictionaryMailpieces.Values)
{
    try
    {
        DataRow[] R = DataTable1.Select("MAILPIECE = " + Mailpiece.MailpieceSetSequenceNumber + " AND (STATUS = 4034 OR STATUS = 4037)", "DAL_DATE desc");
        if (R != null && R.Length > 0)
        {
        }
    }
    catch
    {
    }
}

Answer 1

Funny there is no "SQL" tag associated with your question. I suggest, you learn how to use the SQL language and its benefits. From what you say, it is likely you are, with your code, creating a lot of Cartesian products, instead of leveraging the Relational Database facilities (joins, indexes, etc.)

Using cross joins of DataTables or Lists or anything similar will always lead to heavy performance degradation, whatever language or platform is used.

That said, you could use LINQ because it's capable of producing smart SQL (dynamically), but you still want to avoid all ToList(), ToArray() and similar extension methods on IEnumerable(T) that summon all the underlying data (keep it enumerable from end to end and leverage "object streaming" whenever possible). If you understand really what is a Relational Database and how to use it efficiently, you will be a better LINQ developer.