It also doesn't strike me as especially expensive. A dumb, brute force query (that is, something in 0(N^2)) wouldn't take so long with only a few million rows.

It also doesn't strike me as especially expensive. A dumb, brute force query (that is, something in 0(N^2)) wouldn't take so long with only a few million rows. So I would just try doing through each row, doing a full table scan to find meetings, and just let that cook for a little while. It's not like you're ingesting gobs and gobs of data in real time :)