Sql to find check Percent of Rollback Segment Used?

Question

I have the following queries to find information about rollback segments.
I want the sql to find % of rollback segment used.
--rollsegs.sql
select SEGMENT_NAME, OWNER, TABLESPACE_NAME, SEGMENT_ID, status
from dba_rollback_segs order by segment_name;
select name, extents, writes, xacts, gets,waits, shrinks, aveactive, status
from v$rollname n, v$rollstat s
where n.usn = s.usn
order by name;
--rolbstat.sql
select name, rssize, hwmsize "High", optsize "Opt", wraps, extends, shrinks,
aveshrink "Aveshr", aveactive "Aveact"
from v$rollname n, v$rollstat s
where n.usn = s.usn
order by name;
set numformat 999999990;

Answer 1

DrBurgs, there was a time when your session was assigned a rollback segment that rollback segment held all the updates performed by your session but by Oracle version 8.1 every transaction executed by your session could be assigned to a different rollback segment.
So every 100,000 or whatever value of N use choose as your commit point could result in a different rollback segment being used. You can use v$rollstat and v$transaction to monitor rollback segment usage while the job is running.
You stated that you had one rollback segment for every tablespace. There is no relation in Oracle between the number of tablespace and the number of rollback segments you should have.
You should choose the number of rollback segments to create based on the expected user load and how large a transaction you need to be able to support. For manually defined rollback segments set the initial extent size and the next extent size equal with pctincrease = 0. Then set optimal to the size you would like each rollback segment to be. This size should be large enough that shrinks do not happen often but small enough that one segment that expands will not result in other rollback segments being able to extend. By using uniform extent size you guarentee that every free extent is usable by any other rollback segment that needs to extend.
With a true warehouse you probably have very little update compared to your select load and the updates are probably load jobs. In this case you may need very few, very large rollback segments to handle the load.
HTH -- Mark D Powell --