Question

I’m trying to get a handle on the amount of memory overhead associated with a .NET DataTable, and with individual DataRows within a table.
In other words, how much more memory does a data table occupy than what would be needed simply to store a properly typed array of each column of data?
I guess there will be some basic table overhead, plus some amount per column, and then again an additional amount per row.

So can anyone give an estimate (and, I guess, explanation!) of each/any of these three kinds of overhead?

Answer 1

Well, don’t forget that a DataTable stores 2? 3? versions of the data – original and updated (possibly one other?). It also has a lot of references since it is cell-based, and boxing for any value-types. It would be hard to quantify the exact memory…

Personally, I very rarely use DataTable – typed POCO classes are a much more sensible bet in my view. I wouldn’t use an array (directly), though – List<T> or BindingList<T> or similar would be far more common.

As a crude measure, you could create a lot of tables etc and look at the memory usage; for example, the following shows a ~4.3 factor – i.e. more than 4 times as expensive, but obviously that depends a lot on the number of columns vs rows vs tables etc:

    // takes **roughly** 112Mb  (taskman)     List<DataTable> tables = new List<DataTable>();     for (int j = 0; j < 5000; j++)     {         DataTable table = new DataTable('foo');         for (int i = 0; i < 10; i++)         {             table.Columns.Add('Col ' + i, i % 2 == 0 ? typeof(int)                                 : typeof(string));         }         for (int i = 0; i < 100; i++)         {             table.Rows.Add(i, 'a', i, 'b', i, 'c', i, 'd', i, 'e');         }         tables.Add(table);     }     Console.WriteLine('done');     Console.ReadLine(); 

vs

    // takes **roughly** 26Mb (taskman)     List<List<Foo>> lists = new List<List<Foo>>(5000);     for (int j = 0; j < 5000; j++)     {         List<Foo> list = new List<Foo>(100);         for (int i = 0; i < 100; i++)         {             Foo foo = new Foo { Prop1 = 'a', Prop3 = 'b',                  Prop5 = 'c', Prop7 = 'd', Prop9 = 'e'};             foo.Prop0 = foo.Prop2 = foo.Prop4 = foo.Prop6 = foo.Prop8 = i;             list.Add(foo);         }         lists.Add(list);     }     Console.WriteLine('done');     Console.ReadLine(); 

(based on)

class Foo {     public int Prop0 { get; set; }     public string Prop1 { get; set; }     public int Prop2 { get; set; }     public string Prop3 { get; set; }     public int Prop4 { get; set; }     public string Prop5 { get; set; }     public int Prop6 { get; set; }     public string Prop7 { get; set; }     public int Prop8 { get; set; }     public string Prop9 { get; set; } }