DBA is a career I'm strongly considering after school, but my limited experience mostly involves some PL/SQL Oracle web programming, some basic PHP/MySQL web pages, and some queries in SQL Server. DBMSs are important for my senior project:
+ a presentation highlighting the pros/cons/features of the more popular ones (Oracle, SQL Server, MySQL, DB2, and PostgreSQL) + choosing a DBMS for our actual project.
I'm not asking "Which is best?", but what are some important differences that you have found in your experiences? I have a handle on the differences between InnoDB and MyISAM, and the features tables from the Wiki db comparison, but there's obviously a lot more to it when you're in the field.
So, besides the easy ones (cost,support, OS's, reports for Oracle and SQL Server), what are the issues that you guys have encountered that make, break, or just add some really nice functions that help make your life easier(or harder) as a DBA?
Lastly, we building the framework for a social network. We're using the free micro-instances from AWS, so although that means under 700MB of RAM and a single core, that puts (I think) the free editions of Oracle and SQL Server on the same footing as the open-source DBMS's. The original plan is a LAMP environment, but after researching the topic above, PostgreSQL sounds like it could be useful, given that a social network would utilize a lot of writes (a benefit of InnoDB, as I understand it), but it also sounded like that's the only engine that it uses, whereas MySQL can use both InnoDB and MyISAM for optimization (and I'm sure Facebook uses MySQL for some good reasons).
tl;dr What are some key differences between DBMS's that you've experienced? If you were building a social network that, ideally, would eventually scale to 1 million users, which would you use?