The first thing I would have done is run the query on the database itself. If LIMIT 10 didn't encounter any issues, then that would immediately make me assume t

The first thing I would have done is run the query on the database itself. If LIMIT 10 didn't encounter any issues, then that would immediately make me assume that the amount of data was causing problems on the web layer. Then it's just a matter of tracing the response back from the call to the database backwards until I find the break.