Re: shrinking rbs?

In article <thd2nb7jerf09a_at_beta-news.demon.nl>, postbus_at_sybrandb.demon.nl says...

 He is partly correct, but mostly incorrect.  You are indeed risking incurring 1555, but not because they are in use, but  because you make them too small. Selects are no transactions and do not  extend the rollback segment.
 His resolution to alter the rollback segment offline and online, would,  AFAIK, not change anything.

I didn't think that sounded right; however, I'm not sure I understand your reason for the "snapshot too old" risk either. Let me outline what I believe our situation was and what I think you're saying and you can correct where I'm having the problem:

1. Our rollback segments started with two extents each and grew from there. Since optsize wasn't set, the rollback segments never shrunk back down and eventually reached their maxextents of 121 (thus, the ora-1628 errors).
2. When I manually shrunk the rollback segments, they went back down to two extents each. Now, I take it, from what you and the our resident dba are telling me, that if there was an active transaction happening at that specific time and if someone else were running long winded queries against the database, then I'd be at risk for the snapshot too old errors. This is because there's a strong possibility that the rollback segment extents the transaction was using just got shrunk out of existance. Do I got that right?

If that is right, I have a bone to pick with Oracle (gee, I'm sure they'll get right on that!). If you're shrinking rollback segments, wouldn't it make sense to *not* remove extents that are actively being used?

Assuming again that #2 is correct - is there a correct method to manually shrink rollback segments without risking the snapshot errors?

I appreciate your time and patience, Sybrand. I know you end up answering a lot of questions. I appreaciate it.

Doug

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Douglas K. O'Leary
Senior System Administrator
dkoleary_at_mediaone.net