Last time I checked, that was around PHP 7.0, it was using chaining for its hash table implementation. One notable thing was that its hash table was also using a more optimal array impl (no hashing) if you were only using numerical consecutive keys starting from zero.
Interesting, I definitely missed some of that, didn’t know about replacement of doubly linked list with arData array for maintaining insertion order. It does still use chaining though, just not with the classical pointers and instead with indexes into an array but indirection is still there for collision cases.
