Raj,

You're assuming that the transactions are lasting long enough
for you to catch them in the rollback segments.

Jared






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Thanks Jared, thats not what I see. I have 20 rollback segments, and at no
point in time, there were more than
4 transactions in the rollback segments. In fact, I happened to see it a
couple of minutes ago.

select usn, xacts from v$rollstat showed me 0 in 19 rollback segments, and
2 in one of them. And I have got alerts in place
to alert me when there are more than 4 transactions in all of the rollback
segments. And yeah, the rollback segments
are online.

Remains a mystery to me.

Raj






  
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segments assigned? 
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                    November 25,  
                    2002 08:59 PM  
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Here's one scenario:

4 transactions, 2 rollback segs

tx 1 - rbs1
tx 2 - rbs 2
tx 3  - rbs 1
tx 4 - rbs 2

tx1 and tx3 finish.

tx2 and tx4 have not yet committed.

Jared






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        Subject:        How are rollback segments assigned?


Hello Friends,

Oracle Parallel Server 8.0.6.2.0 on Solaris 2.6 Nodes

We were having some locking and rollback issues, and I set up some scripts
to alert me in case there are more than 4 transactions in the rollback
segments, and more than 1 in any of the rollback segments.

Select sum(xacts) from v$rollstat  --- Alert if more than 4, condition set
to exclude system rollback
where usn != 0

Select count(*) from v$rollstat          --- Alert if more than 0, where
condition to exclude system rollback
where xacts >=2
and    usn != 0

We have 20 rollback segments, and there is very minimal DML activity on
this database. I happened to see a scenario where all rollback segments
had
0 transactions, except for one which had 2 in them. Under what scenario,
can this happen?

I thought the criteria for assigning rollback segments to transactions was
1. If object in system tablespace, use system rolback segment
2. Use the one with the least number of active transactions
3. If 2 or more rollback segments fit the second criteria, use the LRU
algorithm.

Thanks
Raj

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