Why does this LINQ query (Id is a property of type long in the Structure object):
IList<Structure> theStructures = new List<Structure>();
public int GetChildrenSlow(Structure aStructure){
IEnumerable<Structure> childrenQuery =
from structure in theStructures
where structure.ParentStructureId == aStructure.Id
select structure;
int count = childrenQuery.Count();
//Functionality continues...
}
Run slower than this one:
IList<Structure> theStructures = new List<Structure>();
public int GetChildrenFast(long aStructureId){
IEnumerable<Structure> childrenQuery =
from structure in theStructures
where structure.ParentStructureId == aStructureId
select structure;
int count = childrenQuery.Count();
//Functionality continues...
}
I am making this call thousands of time (recursively) and using the property is much slower than using the long directly. If I pull the Id out and store it in a long variable before I execute the LINQ command the speed is pretty much equivalent to the speed of GetChildrenFast. Why is using an object property in LINQ slower than using a primitive?
Working Example:
namespace ConsoleApplication1
{
class Structure
{
public int Id
{
get; set;
}
public int ParentStructureId
{
get; set;
}
}
class Program
{
private IList<Structure> theStructures = new List<Structure>();
public Structure FirstStructure
{
get; set;
}
private int FastCountStructureChildren(long aStructureId)
{
IEnumerable<Structure> childrenQuery =
from structure in theStructures
where structure.ParentStructureId == aStructureId
select structure;
int count = childrenQuery.Count();
foreach(Structure childStructure in childrenQuery)
{
count += FastCountStructureChildren(childStructure.Id);
}
return count;
}
private int SlowCountStructureChildren(Structure aStructure)
{
IEnumerable<Structure> childrenQuery =
from structure in theStructures
where structure.ParentStructureId == aStructure.Id
select structure;
int count = childrenQuery.Count();
foreach(Structure childStructure in childrenQuery)
{
count += SlowCountStructureChildren(childStructure);
}
return count;
}
public void BuildStructure()
{
FirstStructure = new Structure{Id = 0, ParentStructureId = -1};
theStructures.Add(FirstStructure);
//The loop only goes to 6000 as any more than that causes
//a StackOverflowException my development machine.
for(int i=1; i<6000; i++)
{
Structure newStructure = new Structure{Id = i,ParentStructureId = i - 1};
theStructures.Add(newStructure);
}
}
static void Main(string[] args)
{
Program program = new Program();
program.BuildStructure();
Stopwatch fastStopwatch = new Stopwatch();
fastStopwatch.Start();
program.FastCountStructureChildren(0);
fastStopwatch.Stop();
Stopwatch slowStopwatch = new Stopwatch();
slowStopwatch.Start();
program.SlowCountStructureChildren(program.FirstStructure);
slowStopwatch.Stop();
Console.WriteLine("Fast time: " + fastStopwatch.Elapsed);
Console.WriteLine("Slow time: " + slowStopwatch.Elapsed);
Console.ReadLine();
}
}
}