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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11/25/2002 07:39 AM
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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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