It appeared they felt we should be impressed that Facebook runs on MySQL not PostgreSQL. … The problem I have, is that Facebook data is worthless.

All of the concentration is on the company, and whether their use case matters (of course it does, at least to them and their customers). But phrases like “runs on” and “uses” are used too loosely, in my opinion.

Even with celebrity endorsements — for example, a basketball player endorsing shoes — at least they use shoes in roughly the same manner as you might. The shoes might not help you play basketball in any appreciable way, but at least “use” means the same for both the basketball player and you.

However, do you think that running a query at [insert big company here] involves just using the “mysql” client, logging in, and running any ad-hoc query you want? I doubt it. I suspect that the data is always spread around in complex ways with complex caches, and there’s a lot of custom supporting code to get the right information from the right cache at the right time. For every new query, they can unleash a team of very good engineers to build the necessary caches, provision the necessary servers, distribute data to the right places, write the code to populate and read the caches appropriately, and integrate it into the general data-movement architecture.

If your environment looks like that, then a lot of the little problems go away. One might complain that Slony is hard to set up; but in an environment like the one above, it’s insignificant. If there’s some missing feature, you can write it. If something is bothering you, you can fix it. People do that all the time with PostgreSQL, and many of those things get released in the community version. For MySQL, they tend to build up as “patch sets” (or forks, some might call them). I suspect that PostgreSQL gets more contributions because it does everything possible to make the process of community contribution smooth — clean code, no copyright assignment requirement, well-defined “commit fests”, community review, and a diverse group of core members, committers, and contributors. PostgreSQL also has a rock-solid foundation, giving developers more confidence to build the features they need without destabilizing the product.

If your environment doesn’t look like that, and you just want to use the product directly, then take advantage of that. Use the product that makes your life easier, helps you catch errors before they become problems, and keeps your data safe. By the time you scale up, you will be using the DBMS in such a radically different way that it almost doesn’t matter what DBMS you started with.