In 2001, at Thomson-Dialog, I worked on a enterprise academic-literature reference service which ran on a large IBM mainframe in a secure datacenter. Of course, the system depended on an Oracle enterprise DBMS. The Dialog system was actually connected to hundreds of other academic databases using varies enterprise connectors but the trillion or so search terms where cached in the local Oracle database for fast lookup using a somewhat complex search GUI. Dialog Web ran, of course, on Enterprise Java Beans (EJBs).
This was a big deep dive for me into the world of large enterprise client/server systems and databases. And, it was working at Dialog, that I decided that enterprise databases and EJBs were not exactly my cup of tea. However, I did learn a lot about how to develop and debug large enterprise systems including Oracle DBMSes.
Then, in 2002, at ForceField, I was working with Oracle DBMSes again using the enterprise ServicePower schedule optimization system running on Sun Solaris boxes. I actually got deeper into the inner workings of Oracle during this job than at Dialog because ForceField was a startup with only 5 engineers doing everything. So, I got deep into setting up Oracle for test and production deployment defining schemas (in DDL), running SQL*Loader, setting up net services and DB connectors, configuring server clusters, doing DB striping across multiple disk drives, setting up audit tables linked to stored procedures and bunch of other DB admin tasks. Even after doing all that, I still didn't really care that much about data management and databases.
Then, in 2004, I was back again using Oracle somewhat indirectly for the Burke Institute's K-Web project. The choice of Oracle was largely driven by the fact that three of the volunteer engineers on the project where from Oracle. So, of course, they installed the Oracle DBMS on a Sun LX50 x86 box running CentOS. Fortunately, I didn't have to get that deep into Oracle this time because the Oracle engineers handled all the DB details.
I haven't used Oracle since and I'm pretty happy about that.
Experiences using this skill are shown below: