Re: Rollback segment space allocation

In article <2jeo0p$b6_at_nwfocus.wa.com> Mike Dickson <mdickson_at_halcyon.com> writes:
>
> The other day I dropped and recreated my rollback segments. I created
> my tablespace with 70M of space, and then I created 10 rollback segments
> using the command:
>
> create rollback segment r? tablespace rbs_tsp
> storage (initial 3M next 3M maxextents 2 pctincrease 0)
>
> I then stopped and started the database, using the new rollback segments.
> I immediately ran a space usage report on the tablespace, which reported
> that 60M were allocated. I was under the impression that when an object
> was created, only the initial extent was pre-allocated. Since this report
> was run before anyone could use the rollback segments. How come 60M were
> allocated, rather than 30M?
>
Contrary to belief, rollback segments should be created with many (smaller) extents. When a user needs to continue writing to a rollback segment after hitting the end of an extent, it will *never* continue in an extent which contains active transactions. Instead, a new extent will get allocated. I would suggest you use:

create rollback segment r? tablespace rbs_tsp storage ( initial 300k next 300k pctincrease 0 minextents 10 );

I have no idea why your rb-segments allocate 2 extents at once. Maybe the tablespace default storage parameter minextents is set to 2 ?

hope this helps,

--

Magnus Lonnroth
Tech.Sales & Consultant
Oracle Sweden
Mail: mloennro_at_se.oracle.com