Performance differences of contiguous vs non-contiguous column indexing?

General Usage Performance
2

That is expected, because the access to memory is not contiguous. It can get much worse:

julia> x = rand(100_000);

julia> y = @view x[1:10_000];

julia> @btime sum($y)
  944.154 ns (0 allocations: 0 bytes)
5030.276331565986

julia> y = @view x[rand(1:100_000,10_000)];

julia> @btime sum($y)
  12.243 μs (0 allocations: 0 bytes)
4984.892231863414

julia>
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