Let’s say we have an instance used by two clients: me and my friend Ivan. Each of us has his own database. Each of us is only reading.

I’m a bad guy, so I’m relentlessly shooting table scans at the db. My tables are also huge, so they don’t fit into memory. Ivan is a nice guy, so all of his queries are covered by an index, so he has no reasons to hit the disk at all.

Will he notice any problems?

AFAIK, I’ll have a bunch of threads sitting there in SUSPENDED state waiting for disk, and not generating too much of a load otherwise, so Ivan should do just fine.