taking python enterprise level?...

mk mrkafk at gmail.com
Thu Mar 4 13:34:39 CET 2010

Philip Semanchuk wrote:
> Well OK, but that's a very different argument. Yes, joins can be 
> expensive. They're often still the best option, though. The first step 
> people usually take to get away from joins is denormalization which can 
> improve SELECT performance at the expense of slowing down INSERTs, 
> UPDATEs, and DELETEs, not to mention complicating one's code and data 
> model. Is that a worthwhile trade? 

I'd say that in more than 99% of situations: NO.

More than that: if I haven't normalized my data as it should have been 
normalized, I wouldn't be able to do complicated querying that I really, 
really have to be able to do due to business logic. A few of my queries 
have a few hundred lines each with many sub-queries and multiple 
many-to-many joins: I *dread the thought* what would happen if I had to 
reliably do it in a denormalized db and still ensure data integrity 
across all the business logic contexts. And performance is still more 
than good enough: so there's no point for me, as of the contexts I 
normally work in, to denormalize data at all.

It's just interesting for me to see what happens in that <1% of situations.

> Depends on the application. As I 
> said, sometimes the cure is worse than the disease.
> Don't worry about joins until you know they're a problem. As Knuth said, 
> premature optimization is the root of all evil.

Sure -- the cost of joins is just interesting to me as a 'corner case'. 
I don't have datasets large enough for this to matter in the first place 
(and I probably won't have them that huge).

> PS - Looks like you're using Postgres -- excellent choice. I miss using it.

If you can, I'd recommend using SQLAlchemy layer on top of 
Oracle/Mysql/Sqlite, if that's what you have to use: this *largely* 
insulates you from the problems below and it does the job of translating 
into a peculiar dialect very well. For my purposes, SQLAlchemy worked 
wonderfully: it's very flexible, it has middle-level sql expression 
language if normal querying is not flexible enough (and normal querying 
is VERY flexible), it has a ton of nifty features like autoloading and 
rarely fails bc of some lower-level DB quirk AND its high-level object 
syntax is so similar to SQL that you quickly & intuitively grasp it.

(and if you have to/prefer writing some query in "low-level" SQL, as I 
have done a few times, it's still easy to make SQLAlchemy slurp the 
result into objects provided you ensure there are all of the necessary 
columns in the query result)


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