alt Hacker News> Your DB isn't going any faster by switching to something else, if that's what you think.
Only true if none of the DB accesses are about stuff that could live as state across requests in a server that wasn't php. Sure, for some of that the DB's caching will be just as good, but for others, not at all.
That is possible, but it sounds unlikely to me.
In most cases you could add a shared cache to fix the problem - e.g. put your shared state in Redis, or in a file that is synced across servers (if its kept as state in a long running process it cannot need to be updated frequently).