I'm not denying that you could have a query that takes hours and is within 10x the speed it should be, just saying that it's very common to have inefficient SQL

I'm not denying that you could have a query that takes hours and is within 10x the speed it should be, just saying that it's very common to have inefficient SQL queries for reporting. I would say it's almost the "default" state unless you do a bit of work. Some more detail here: https://news.ycombinator.com/item?id=19150971 https://news.ycombinator.com/item?id=19150971 There are many interesting queries that don't touch all the data in the database. The 'cat' thing was basically assuming the worst case, e.g. as a sanity check.