Scala collection memory footprint characteristics

Question

There is a handy page about performance characteristics of the Scala collection classes. Is there similar data on memory footprint?

I have a situation where I'm concerned about memory use and would like to factor this in my choice of collection to use. For instance, between Array[Array[T]] and Vector[Vector[T]].

Answer 1

Here is what I've found out by filling up those respective immutable sequences with 1,000,000 objects on 2.9.0. I had them all point to the same object to factor out the size of the content.

• Array: 1x (baseline 4,000,016 bytes on 32 bits; 8,000,024 on 64 bits)
• Vector: 1.17x
• List, Queue, Stack: 4x
• evaluated Stream: 10x

System.gc was called then triggered heap dump then opened in Eclipse MAT.

Based on that Array and Vector are pretty closed.

Answer 2

You could start with a simple generation of multiple, multidimensional Vectors and Arrays of different size:

val vMin = Vector.fill (10  , 10)(9)
val vMed = Vector.fill (1000, 10)(9)
val aMed =  Array.fill (1000, 10)(9)

10 Arrays of 10 Arrays of Ints with Value 9, 1000 such Arrays, 1000 such Vectors ...

To measure the size, you could use

$JAVA_HOME/bin/jvisualvm