Hi!
It seems from my tinkering that MySQL query cache handling is circumvented via HandlerSocket.
On busy systems (I assume we talk about busy systems, as discussion is about HS) query cache is usually eliminated anyway. Either by compiling it out, or by patching the code not to use qcache mutexes unless it really really is enabled. In worst case, it is just simply disabled. :)
So if you update/insert/delete via HandlerSocket, then query via SQL your not guarenteed to see the changes unless you use SQL_NO_CACHE.
You are probably right. Again, nobody cares about qcache at those performance boundaries.
Domas