[beagle3]

> When you write Java in a C like syntax

And C is faster still when you write it with Fortran like (column order, and "restrict" mostly) semantics.

An old mentor said to me 30 years ago that "A good programmer writes FORTRAN no matter what language they are using" (he was referring to speed of execution in the context of "good"). It seemed super funny at the time, but there's a lot of truth in that.

[ryl00]

Why does column order matter? If you translate to the equivalent C/C++ row-major order, it should be laid out in memory the same way.

[beagle3]

What do you mean by "if you translate to C/C++ row major order?"

What I meant was: In FORTRAN, you idiomatically do Struct-Of-Array=Column-Major order by default, In C/C++ you do Array-of-Struct or Array-of-Pointer-to-Struct (both of which are Row-Major) by default. The former tends to be much more efficient than the latter in computational code.

It turns out that, often and especially in computationally intensive code, only a small number of fields of an object/record are used in every part of the computation pipelines, but almost all records are.

As a result, if you do your data in column major order, then the cache usage patterns reflect that - whereas if you are in row major order, a lot more field get loaded into cache when they are not needed (thus, much lower cache utilization and lower performance).

FORTRAN did not have structures until quite late (FORTRAN-95 has them for sure, but IIRC FORTRAN-77 and earlier didn't). Thus, the idiomatic way to do stuff is have an SoA=Coiumn-Major implementation, rather than the C/C++ AoS=Row-Major order.

Furthermore, FORTRAN didn't have any pointers. As a result, most code was written with very little pointer chasing / foreign key reference chasing -- which also contributes to efficient use of cache and memory bandwidth.