What does dotTrace Performance Profiler mean by [Garbage collection]?

Question

What does [Garbage collection] mean in this pic? And the "20 calls" thing?

I mean, how can I figure out why GC took so long? Was it collecting a lot of small objects? A single big one? Any hints as to how to optimize this at all?

The code in question is:

private void DeserializeFrom(SerializationInfo info)
{
    Width = info.GetInt32("width");
    Height = info.GetInt32("height");
    var data = (List<byte>)info.GetValue("cells", typeof(List<byte>));
    cells = new Cell[physicalSize.Width, physicalSize.Height];
    int pos = 0;
    for (int x = 0; x < physicalSize.Width; x++)
    {
        for (int y = 0; y < physicalSize.Height; y++)
        {
            cells[x, y] = new Cell();
            if (x < Width && y < Height)
            {
                cells[x, y].HasCar = data[pos];
                pos++;
            }
        }
    }
}

Nothing too fancy. I suspect the culprit is the big List<byte> object, but I thought collecting a single, big object is supposed to be instant (as opposed to collecting a bunch of small objects).

Answer 1

If you want to find out what is causing GCs, what objects are being allocated and collected, you can do it via dotMemory. Here is a tutorial that explains how to optimize memory traffic: https://confluence.jetbrains.com/display/NETCOM/Tutorial+3+-+How+to+Optimize+Memory+Traffic+with+dotMemory

Answer 2

A little late to the party but if you are using .Net then you are using managed code, which basically means that the .Net runtime disposes your objects accordingly so you don't have memory leaks as opposed to C or C++.

Garbage Collection is whenever the runtime takes a time to manage the allocation and release of memory for the application. In this case that is what's taking place.

Please take a look at this filter that can be used with doTrace (I have version 6) so that you can analyze garbage collection and determine when it might be blocking your execution. https://www.jetbrains.com/profiler/help/CLR_Activity.html