Temporary tables can be dropped automatically as the process that created them leaves scope (the user logs off or breaks the connection). Global temp tables are dropped automatically when all processes that have referenced them leave scope. I don't have hard evidence to back this up because I've never done quite what you're doing, but I suspect that when you issue the drop statement on the global temp table, it's doing some kind of check against existing sessions(and with that many databases I'll bet you have an equally high number of sessions going) to see if anyone is referencing prior to dropping it. If you're not referencing the temp table by multiple sessions, there's no reason to make it a global temp table.