Re: Rollback segment used in exclusive mode : Why ?

Hi Emmanuel,
I'm not sure what's happening, so these are my 'hints' I can think of two scenarios.
The first scenario is the use of the set transaction command places an exclusive lock on the dictionary record for the rollback segment. Your remark about the Lock Manager seems to confirm that, and it is definitely something I am going to repeat on Monday. If this is true, I consider that as a bug, and you would think Oracle does too. The second scenario is your rollback segment config. The parameter transactions per rollback segments usually is derived from the sessions (or processes) parameter, divided by the number of public rollback segments. Probably your rollback segments are private, so that shouldn't be the problem. I believe however you need to check on the current value of transactions_per_rollback_segments, because if that parameter equals 1 that is the explanation of your problem.
The only other thing, and that probably is unlikely too: as far as I understand the rollback segments, any new transaction will use a different extent from the previous one. If you have minimal extents (where 2 is the absolute minimum), there could also be a situation of no extents being available to start the transaction.
Personally, I would rather refer to v$rollstat to see what is happening, one of the columns is XACT, the number of active transactions.

To be continued

Hth,
Sybrand Bakker, Oracle DBA

Emmanuel Guyot wrote in message <7kg9kf$hpr$1_at_wanadoo.fr>...
>Each of my rollback segment is used in exclusive mode. I mean that only one
>transaction can use it. For example, if I force the use of one Rollback
>Segment (set transaction use rollback segment ...) I update a table and I
>don't quit.
>If I do the same thing from another session, the second one is locked!
>
>If I verify with Lock Manager, it confirms that the rollback segment is
used
>in exclusive mode.
>
>The question is Why! I've asked the Oracle support but they don't know.
>
>I've dropped and created back the rollback segment (create rollback segment
>XXX tablespace YYYY) but the problem still occurs.
>
>Please give me any hint.
>
>N.B. : My OS is Solaris 2.5.1, with Oracle 7.3.3
>
>E.G.
>
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Received on Sat Jun 19 1999 - 11:36:38 CDT