Max Array Length in Julia

Question

I can create an array of a million elements like this:

Array(1:1_000_000)
Vector{Int64} with 1000000 elements

but if I try to create an array of a billion elements I get this:

Array(1:1_000_000_000)
Julia has exited.
Press Enter to start a new session.

Is Julia not able to handle a billion elements in an array or what am I doing wrong here?

Answer 1

You are creating an Array of Int64, each of which needs to be stored in memory:

julia> sizeof(3)
8

So at some point you're bound to run out of memory - this is not due to some inherent limit on the number of elements in an array, but rather the size of the overall array, which in turn depends on the size of each element. Consider:

julia> sizeof(Int8(3))
1

julia> [Int8(1) for _ in 1:1_000_000_000]
1000000000-element Array{Int8,1}:
 1
 1
 1
 ⋮
 1
 1
 1

so filling the array with a smaller data type (8-bit rather than 64-bit Integer) allows me to create an array with more elements.