How to: Use Pageable Collections

• Nov 21, 2018
• 3 minutes to read

This example provides a memory usage comparison between the XPCollection and XPCursor instances.

Creating and persisting the objects in the database.

C#

int i;
string dataString = new String('?', 1024);
Session.DefaultSession.ClearDatabase();
Console.WriteLine("Creating objects");
// The loop here creates 1000 objects.
for(i = 0; i<1000; ++i) {
    SampleObject theObject = new SampleObject();
    theObject.Data = dataString;
    theObject.Save();
}

VB.NET

Dim i As Integer
Dim dataString As New String("?", 1024)
Session.DefaultSession.ClearDatabase()
Console.WriteLine("Creating objects")
Dim theObject As SampleObject
' The loop here creates 1000 objects.
For i = 1 To 1000
    theObject = New SampleObject()
    theObject.Data = dataString
    theObject.Save()
Next

Then we iterate through the contents of the XPCollection and XPCursor and modify the values of the retrieved objects. We assess the amount of memory allocated every time one hundred objects have been modified.

C#

GC.Collect();
i = 0;
Console.WriteLine("Processing objects with XPCursor");
XPCursor cursor = new XPCursor(Session.DefaultSession, typeof(SampleObject));
cursor.PageSize = 100;
// Loop through all the objects.
foreach(SampleObject theObject in cursor) {
    theObject.Data = new String('!', 1024);
    theObject.Save();
    ++i;
     // Every 100 objects write out memory used.
    if(i % 100 == 0)
Console.WriteLine(String.Format("Object {0}, memory allocated {1}", i, GC.GetTotalMemory(true)));
}

GC.Collect();
i = 0;
Console.WriteLine("Processing objects with XPCollection");
using(XPCollection collection = new XPCollection(Session.DefaultSession, typeof(SampleObject))) {
// Loop through all the objects.
    foreach(SampleObject theObject in collection) {
        theObject.Data = new String('@', 1024);
        theObject.Save();
        ++i;
        if(i % 100 == 0)
            // Every 100 objects write out memory used.
            Console.WriteLine(String.Format("    Object {0}, memory allocated {1}", i, 
              GC.GetTotalMemory(true)));
    }
}

VB.NET

GC.Collect()
 i = 0
 Console.WriteLine("Processing objects with XPCursor")
 Dim cursor As New XPCursor(Session.DefaultSession, GetType(SampleObject))
 cursor.PageSize = 100
' Loop through all the objects.
 For Each theObject In cursor
      theObject.Data = New String("!", 1024)
      theObject.Save()
      i = i + 1
      ' Every 100 objects write out memory used.
      If i Mod 100 = 0 Then
          Console.WriteLine(String.Format("  Object {0}, memory allocated {1}", i, _
            GC.GetTotalMemory(True)))
      End If
Next theObject

GC.Collect()
i = 0
Console.WriteLine("Processing objects with XPCollection")
' Loop through all the objects.
For Each theObject In New XPCollection(Session.DefaultSession, GetType(SampleObject))
    theObject.Data = New String("@", 1024)
    theObject.Save()
    i = i + 1
    ' Every 100 objects write out memory used.
    If i Mod 100 = 0 Then
  Console.WriteLine(String.Format("Object {0}, memory allocated {1}", i, GC.GetTotalMemory(True)))
    End If
Next theObject

The table below shows the result:

Processing objects with XPCursor	Processing objects with XPCollection
Object 100, memory allocated 382752 Object 200, memory allocated 389152 Object 300, memory allocated 395552 Object 400, memory allocated 386336 Object 500, memory allocated 392736 Object 600, memory allocated 386336 Object 700, memory allocated 392736 Object 800, memory allocated 386336 Object 900, memory allocated 392736 Object 1000, memory allocated 386036	Object 100, memory allocated 2568928 Object 200, memory allocated 2568504 Object 300, memory allocated 2568504 Object 400, memory allocated 2568504 Object 500, memory allocated 2568504 Object 600, memory allocated 2568492 Object 700, memory allocated 2568492 Object 800, memory allocated 2568492 Object 900, memory allocated 2568492 Object 1000, memory allocated 2568492

From the output you can see that the XPCursor has significantly improved the way in which memory is allocated for the collection’s contents.