Almost 10 years ago, we started working with Open Source databases, and looked at MySQL and PostgreSQL. Back then, the feature list was night and day, MySQL was fast, lightning fast, on quick reads, and extremely slow on complicated joins. PostgreSQL was much slower on the simple reads, but the referential integrity features, like delete cascades made the writes/deletes/updates much faster. Most of the commentary at the time focused on transactions, but PostgreSQL focused on correctness.
Let me give you an example. Assume I have my website products put into categories for a custom product display system (this was a common problem for someone building SEO sites for products back in 2001-2004). If I wanted my products to exist in multiple categories, I created an intermediate mapping table, and everyone that uses a ORM system is probably nodding their head right now. But here was the neat thing, in PostgreSQL, I just set the mapping table’s references to the Ids as NOT NULL ON DELETE CASCADE. Now, if I delete a category, I don’t have to delete everything from the mapping table, it automatically deletes the entry whenever the category is deleted (and same thing for a product).
Now, the MySQL guys are thinking, lazy programmer, just delete from the mapping table when you delete, and we keep our faster database, or use the slow relational table systems if you are lazy. That’s all correct, but assume I’m updating this 2001 site to support a new product/category tagging feature. I want it fast, so I create a table of tags (with some descriptions for my SEO purposes), and two (or more) mapping tables. Now on my PostgreSQL website, no big deal, I just make these maps ON DELETE CASCADE, and when I delete a category, it deletes the tags as well. On the MySQL site, I have to dig into the code where I deleted the category, and update it to delete the tags. This is fine if I built it, but what if that chunk was built by my summer intern who was learning programming at the time, now it’s a pile of spaghetti code, it works, but it’s ugly, and now I have to fix it.
Now, in 2009, MySQL has tables with referential integrity, and PostgreSQL is way faster. I have a library of pl/pgsql code I have written over the years for PostgreSQL, some of which I updated for the new features in Postgresql 8.x, some of which still dates back to the limitations of Postgresql 7.3. I have SEO efficient code so I never have to worry about HTML friendly naming schemes for URLs, and other things. Meanwhile, MySQL has added cool features for the open source world of quick and dirty code, and PostgreSQL has tried to aim to please DBAs with awesome tuning parameters. As a result, their is a wealth of awesome Open Source code developed in the past 8 years, but it’s all on MySQL. Even when it’s ported to PostgreSQL, it’s using PostgreSQL as a fake MySQL, as in we don’t do ON DELETE CASCADE, we still delete from the mapping table.
And PostgresSQL fixed the speed problems, 8.3 is FAST, and the new 8.4 is probably FASTER, but we don’t take advantage of it because our code is all on MySQL. Just another reminder that Worse Really Is Better!