When you can't query your DB, you hit your resident memory cache. Redis, Memcached, etc. You probably have background threads that do cache invalidation, queue management, etc.
You frequently have to be more reliable than your database.
> he responded that it was not required in a web context, as web servers already have threads per request so its a mute point.
I use multiple threads in a single request flow frequently. Dispatching requests to other services or data stores, updating in-memory caches or queues (not Redis, but living within the app itself), etc. It's an important tool.
> Ok now you have just thrown away one of the main benefits of PHP. Remember, Rasmus is a C programmer, not a PHP programmer, so he wanted to leverage that HUGE library of existing C-code from his new scripting language, from the very beginning, deliberately by design.
Good for him. I don't see why that matters for anyone else. It's ugly and inconsistent, takes time to memorize, and leads to errors.
> Yes because each request is a synchronous thread, as described above above. By design.
This limits you to writing basic CRUD. And so many other languages offer this.