[rurban]

Python, ruby, php hash tables are roughly 2x slower. perl5's being the worst maybe 4x slower.

Damn fast is only relative. It's damn fast compared to the previous implementations. Wikipedia even dares to say that the worst hash tables of all, perl5, is one of the very best. Bias all over.

SIMD optimized hash tables, such as the Swiss tables tricks have the potential to be much faster than khash. And khash is not cache oblivious at all, with its double hashing scheme.

[sametmax]

Does it preserves insertion order ?

[rurban]

Of course not. hash table iteration should assume random order, otherwise it's a security risk or performance nightmare.