A DB2(R) Fix Pack contains updates and fixes for problems (Authorized Program Analysis Reports, or "APARs"). These APARs address problems found during testing at IBM(R), as well as fixes for problems reported by customers.  
DB2 Version 9.1 for Linux, UNIX, and Windows APARs are published in technote 1255607
http://www.ibm.com/support/docview.wss?uid=swg21255607