Question

In my Rails App I’ve several models dealing with assets (attachments, pictures, logos etc.). I’m using attachment_fu and so far I have 3 different tables for storing the information in my MySQL DB.

I’m wondering if it makes a difference in the performance if I used STI and put all the information in just 1 table, using a type column and having different, inherited classes. It would be more DRY and easier to maintain, because all share many attributes and characteristics.

But what’s faster? Many tables and less rows per table or just one table with many rows? Or is there no difference at all? I’ll have to deal with a lot of information and many queries per second.

Thanks for your opinion!

Answer 1

Many tables and fewer rows is probably faster.

That’s not why you should do it, though: your database ought to model your Problem Domain. One table is a poor model of many entity types. So you’ll end up writing lots and lots of code to find the subset of that table that represents the entity type you’re currently concerned with.

Regular, accepted, clean database and front-end client code won’t work, because of your one-table-that-is-all-things-and-no-thing-at-all.

It’s slower, more fragile, will multiply your code all over you app, and makes a poor model.

Do this only if all the things have exactly the same attributes and the same (or possibly Liskov substitutable) semantic meaning in your problem domain.

Otherwise, just don’t even try to do this.

Or if you do, ask why this is any better than having one big Map/hash table/associative array to hold all entities in your app (and lots of functions, most of them duplicared, cut and paste, and out of date, doing switch cases or RTTI to figure out the real type of each entity).