changes/bugs may fail your 11g upgrade

For OLAP type databases or running  complicated batch jobs.
1. here are two bugs 8477973 and 4926618

8477973 Multiple open DB links / ORA-2020 / distributed deadlock possible 

Impact: hang your sql session

4926618 Excessive CPU on HASH UNIQUE when repeated

Good news, both of them are fixed in 11.2.0.2

Impact: x times slower your UPDATE statement.  Especially updating more than 1 million rows. The more rows more greater times.  In my case, 21 minutes becomes  8 hours .



2. new parameter db_ultra_safe:  DATA_AND_INDEX comes with significant overhead. For my INSERT case, it is 7x slower.


Spent weeks of effort to come to above findings.  Hope it help preventing from happening to you . Cheers!