With the first fundamental fact - don't think that all DBMSes are (or should be) the same. If one knows well one particular DBMS...

You can check my Oracle wiki article describing basic documentation and giving some basic resource links in internet:

http://wiki.oracle.com/page/Troubleshooting+-+Database

Gints Plivna

http://www.gplivna.eu

There are tons of websites explaining Oracle.

You can start for example with my Oracle wiki article

http://wiki.oracle.com/page/Troubleshooting+-+Database

to get the idea how documenation is organized and what are just a few...