mk wrote: > D'Arcy J.M. Cain wrote: >> I keep seeing this statement but nothing to back it up. I have created >> many apps that run on Python with a PostgreSQL database with a fully >> normalized schema and I can assure you that database joins were never >> my problem unless I made a badly constructed query or left off a >> critical index. > > I too have done that (Python/PGSQL), even adding a complicated layer of > SQLAlchemy on top of it and have not had issue with this: when I > profiled one of my apps, it turned out that it spent most of its > computation time... rendering HTML. Completely unexpected: I expected DB > to be bottleneck (although it might be that with huge datasets this > might change). > > Having said that, re evidence that joins are bad: from what I've *heard* > about Hibernate in Java from people who used it (I haven't used > Hibernate apart from "hello world"), in case of complicated object > hierarchies it supposedly generates a lot of JOINs and that supposedly > kills DB performance. > > So there *may* be some evidence that joins are indeed bad in practice. > If someone has smth specific/interesting on the subject, please post. > I suspect that this myth is propagated from the distributed database world: joining tables across two different servers can indeed be problematic from a performance point of view.
However, the classic advice in database design is to start with a normalized design and then vary it only if you need to for performance reasons (which will also involve taking a hit on the coding side, especially if updates are involved). regards Steve -- Steve Holden +1 571 484 6266 +1 800 494 3119 PyCon is coming! Atlanta, Feb 2010 http://us.pycon.org/ Holden Web LLC http://www.holdenweb.com/ UPCOMING EVENTS: http://holdenweb.eventbrite.com/ -- http://mail.python.org/mailman/listinfo/python-list
