Anytime you’re working with large result sets the database is going to
be more efficient. Using the middle tier makes a lot of sense in some
cases, but putting that data into code is in some ways throwing away the
very thing DBs are good at – handling large sets of data. For instance,
an app I’ve worked on needed to calculate sums of previously paid
quantities (along with a bunch of other stuff), for a few thousand
records at a time. Doing it row by row took more than 10 minutes (on a
dual xeon with 6gb of ram). By switching the calculations to be based on
the results of a join, it went down to 10-15 seconds. I think this is a
decent illustration of a case where taking advantage of the data layer
was really the right thing to do, rather than building and tearing down
50,000 individual database hits (even with connection pooling) from the
middle tier.
Every app is different, and so there’s never going to be a rule of
middle tier vs data tier.
DISCLAIMER: I’m a RoR newbie who’s been lurking on the list. If I said
something that doesn’t hold true for RoR, I apologize in advance, and
please ignore me 