Database is slow

Question

Hi,
we have migrated database from single instance to 2 node RAC recently and since then we have been observing degardation of perfromance.The mostly observed wait events on the database are buffer busy waits and db file sequential read.another observation is that library cache miss rate always hangs above 60%.
It'a documentum application.
The application is using only two tablespaces one for data and another for indexes.Kindly suggest the way in whch i can boost up the perfromance.
vamsi

Answer 1

Hello,
Well moving from single install to RAC is more then just high availability. You need to do some tuning, and I mean serious tuning.
The are huge amounts of resources out on the web about this. In short here is what you are facing:
"The main way to reduce buffer busy waits is to reduce the total I/O on the system. This can be done by tuning the SQL to access rows with fewer block reads (i.e., by adding indexes). Even if we have a huge db_cache_size, we may still see buffer busy waits, and increasing the buffer size won't help.
The resolution of a "buffer busy wait" events is one of the most confounding problems with Oracle. In an I/O-bound Oracle system, buffer busy waits are common, as evidenced by any system with read (sequential/scattered) waits in the top-five waits."
Hope this helps you get on your way. Check in the database forums for more help, or just have your local DBA tune the database. If he you are running enterprise edition then you should have access to the performance tools, including SQL Tuning advisor, Segment advisor.
When you generate an snapshot report, check if you don't have any ITL waits, see what segments and block the database is hot for. see what SQL statement are hot(meaning how many times its been executed, and how many buffer is reads every time).
Hope this helps.
Jan