If you work on the RDBMS kernel, your debugging and reverse engineering skills will certainly be put to the test. The deeper knowledge is somewhat silo'd, so in addition to comfort in system level C, you should be comfortable walking up to people's desks to get answers rather than expecting things to make sense over email. The RBDMS kernel is pretty deep so people spend time in specific areas. I can still regurgitate function names and acronyms and code paths for the areas I worked in. I spend some time there after college and learned quite a bit. The single biggest take away was that it removed any fear I ever had of looking at someone else's code. Lots of good people I still keep in touch with.