Question

I have huge amont of geographic data represented in simple object structure consisting only structs. All of my fields are of value type.

public struct Child
{
   readonly float X;
   readonly float Y;
   readonly int myField;
}

public struct Parent
{
   readonly int id;
   readonly int field1;
   readonly int field2;
   readonly Child[] children;
}

The data is chunked up nicely to small portions of Parent[]-s. Each array contains a few thousands Parent instances. I have way too much data to keep all in memory, so I need to swap these chunks to disk back and forth. (One file would result approx. 2-300KB).

What would be the most efficient way of serializing/deserializing the Parent[] to a byte[] for dumpint to disk and reading back? Concerning speed, I am particularly interested in fast deserialization, write speed is not that critical.

Would simple BinarySerializer good enough?
Or should I hack around with StructLayout (see accepted answer)? I am not sure if that would work with array field of Parent.children.

UPDATE: Response to comments – Yes, the objects are immutable (code updated) and indeed the children field is not value type. 300KB sounds not much but I have zillions of files like that, so speed does matter.

Answer 1

BinarySerializer is a very general serializer. It will not perform as well as a custom implementation.

Fortunately for your, your data consists of structs only. This means that you will be able to fix a structlayout for Child and just bit-copy the children array using unsafe code from a byte[] you have read from disk.

For the parents it is not that easy because you need to treat the children separately. I recommend you use unsafe code to copy the bit-copyable fields from the byte[] you read and deserialize the children separately.

Did you consider mapping all the children into memory using memory mapped files? You could then re-use the operating systems cache facility and not deal with reading and writing at all.

Zero-copy-deserializing a Child[] looks like this:

byte[] bytes = GetFromDisk();
fixed (byte* bytePtr = bytes) {
 Child* childPtr = (Child*)bytePtr;
 //now treat the childPtr as an array:
 var x123 = childPtr[123].X;

 //if we need a real array that can be passed around, we need to copy:
 var childArray = new Child[GetLengthOfDeserializedData()];
 for (i = [0..length]) {
  childArray[i] = childPtr[i];
 }
}